Active Q-switched Fiber Lasers with Single and Dualwavelength Operation

A brief explanation on Q-switched fiber laser operating principle for active technique in terms of operation characteristics is presented. Experimental analysis of proposed pulsed fiber lasers by the active Q-switched technique is demonstrated. Experimental setups include the use of Er/Yb doped fiber as a gain medium and an acousto-optic modulator as cavity elements. Setup variations include the use of fiber Bragg gratings for wavelength selection and tuning and Sagnac interferometer for wavelength selection in single wavelength operation and for cavity loss adjustment in dual wavelength operation. The experimental analysis of principal characteristics of single-wavelength operation of the fiber laser and cavity loss adjustment method for dual-wavelength laser operation are discussed

In-Fiber Acousto-Optic Interaction Based on Flexural Acoustic Waves and Its Application to Fiber Modulators

The design and implementation of in-fiber acousto-optic (AO) devices based on acoustic flexural waves are presented. The AO interaction is demonstrated to be an efficient mechanism for the development of AO tunable filters and modulators. The implementation of tapered optical fibers is proposed to shape the spectral response of in-fiber AO devices. Experimental results demonstrate that the geometry of the tapered fiber can be regarded as an extra degree of freedom for the design of AO tunable attenuation filters (AOTAFs). In addition, with the objective of expanding the application of AOTAFs to operate as an amplitude modulator, acoustic reflection was intentionally induced. Hence, a standing acoustic wave is generated which produces an amplitude modulation at twice the acoustic frequency. As a particular case, an in-fiber AO modulator composed of a double-ended tapered fiber was reported. The fiber taper was prepared using a standard fusion and pulling technique, and it was tapered down to a fiber diameter of 70 μm. The device exhibits an amplitude modulation at 2.313 MHz, which is two times the acoustic frequency used (1.1565 MHz); a maximum modulation depth of 60%, 1.3 dB of insertion loss, and 40 nm of modulation bandwidth were obtained. These results are within the best results reported in the framework of in-fiber AO modulators

Supermode noise of harmonically mode-locked erbium fiber lasers with composite cavity

The supermode noise of a harmonically mode-locked erbium-doped fiber laser with composite cavity is investigated both theoretically and experimentally. We propose a simple model based on the transfer function of the composite cavity. From this model, the frequencies of the cavity modes and their frequency-dependent losses are determined. A comprehensive experimental study of the composite cavity laser is carried out, covering a wide range of path-length differences between both arms of the fiber interferometer that form the composite cavity. Experimental results are in good agreement with our model. In particular, the path length difference determines periodic frequency windows within which supermodes of the composite cavity are observed. Outside these windows, supermodes are not detectable. Our results show quite remarkably that, although the number of supermodes is reduced with respect to the simple cavity, no measurable reduction of the overall supermode noise is obtained, contrary to what has recently been suggested.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Experimental study of supermode noise of harmonically mode-locked erbium-doped fibre lasers with composite cavity

An experimental study of supermode noise of harmonically actively mode-locked erbium-doped fibre lasers in the composite-cavity configuration is reported. Our study shows that the number of supermodes is reduced, as expected. However, this reduction is by far less efficient than what was previously reported. In particular, we found in measured RF spectra that supermodes appear in wide periodic frequency windows. Our most significant result is that, contrary to what has been previously reported, we did not measure in the composite-cavity laser any significant reduction of the overall supermode noise in comparison with the standard single-cavity configuration. © 2002 Elsevier Science B.V. All rights reserved.info:eu-repo/semantics/publishe

Sagnac with Double-Sense Twisted Low-Birefringence Standard Fiber as Vibration Sensor

In this work, we study a double-sense twisted low-birefringence Sagnac loop structure as a sound/vibration sensing device. We study the relation between the adjustments of a wave retarder inside the loop (which allows controlling the transmission characteristic to deliver 10, 100, and 300 μW average power at the output of the system) and the response of the Sagnac sensor to vibration frequencies ranging from 0 to 22 kHz. For a 300 m loop Sagnac, two sets of experiments were carried out, playing at the same time all the sound frequencies mixed for ∼1 s, and playing a sweep of frequencies for 30 s. In both cases, the time- and frequency-domain transmission amplitudes are larger for an average power of 10 μW, and smaller for an average power of 300 μW. For mixed frequencies, the Fourier analysis shows that the Sagnac response is larger for low frequencies (from 0 to ∼5 kHz) than for high frequencies (from ∼5 kHz to ∼22 kHz). For a sweep of frequencies, the results reveal that the interferometer perceives all frequencies. However, beyond ∼2.5 kHz, harmonics are present each ∼50 Hz, revealing that some resonances are present. The results about the influence of the power transmission through the polarizer and power emission of laser diode (LD) on the Sagnac interferometer response at high frequencies reveal that our system is robust, and the results are highly reproducible, and harmonics do not depend on the state of polarization at the input of the Sagnac interferometer. Furthermore, increasing the LD output power from 5 mW to 67.5 mW allows us to eliminate noisy signals at the system output. in our setup, the minimum sound level detected was 56 dB. On the other hand, the experimental results of a 10 m loop OFSI reveal that the response at low frequencies (1.5 kHz to 5 kHz) is minor compared with the 300 m loop OFSI. However, the response at high frequencies is low but still enables the detection of these frequencies, yielding the possibility of tuning the response of the vibration sensor by varying the length of the Sagnac loop

Characterizing the Statistics of a Bunch of Optical Pulses Using a Nonlinear Optical Loop Mirror

We propose in this work a technique for determining the amplitude distribution of a wave packet containing a large number of short optical pulses with different amplitudes. The technique takes advantage of the fast response of the optical Kerr effect in a fiber nonlinear optical loop mirror (NOLM). Under some assumptions, the statistics of the pulses can be determined from the energy transfer characteristic of the packet through the NOLM, which can be measured with a low-frequency detection setup. The statistical distribution is retrieved numerically by approximating the solution of a system of nonlinear algebraic equations using the least squares method. The technique is demonstrated numerically in the case of a packet of solitons

Comparative proteomic analysis of blood eosinophils reveals redox signaling modifications in patients with FIP1L1-PDGFRA-associated chronic eosinophilic leukemia

International audienceThe FIP1L1-PDGFRA (F/P) fusion gene, which was identified as a recurrent molecular finding in hypereosinophilic syndrome (HES), lead to a constitutively increased tyrosine kinase activity of the fusion protein. Despite data obtained in animals or cell lines models, the mechanisms underlying the predominant eosinophil lineage targeting and the cytotoxicity of eosinophils in this leukemia remain unclear. To define more precisely intrinsic molecular events associated with F/P gene, we performed a proteomic analysis comparing F/P+ eosinophils (F/P-Eos) and eosinophils from healthy donors (C-Eos). Using 2D-DIGE and mass spectrometry techniques, we identified 41 proteins significantly overexpressed between F/P-Eos and C-Eos. Among them, 17.8% belonged to the oxidoreductase family. We further observed a down-expression of peroxiredoxin-2 (PRX-2) and an overexpression of src-homology-2 domain containing tyrosine phosphatase (SHP-1), enzymes regulating PDGFR downstream pathways, and especially intracellular reactive oxygen species (ROS) production. This profile, confirmed in immunoblot analysis, appears specific to F/P-Eos compared to controls and patients with idiopathic HES. In this clonal disorder possibly involving a pluripotent hematopoietic stem cell, we postulate that the well documented relationships between PDGFRA downstream signals and intracellular ROS levels might influence the phenotype of this leukemia

Glial-cell-mediated re-induction of the blood-brain barrier phenotype in brain capillary endothelial cells: A differential gel electrophoresis study

International audienceIn the neurovascular unit, brain microvascular endothelial cells develop characteristic barrier features that control the molecular exchanges between the blood and the brain. These characteristics are partially or totally lost when the cells are isolated for use in in vitro blood-brain barrier (BBB) models. Hence, the re-induction of barrier properties is crucial for the relevance of BBB models. Although the role of astrocyte promiscuity is well established, the molecular mechanisms of re-induction remain largely unknown. Here, we used a DIGE-based proteomics approach to study endothelial cellular proteins showing significant quantitative variations after BBB re-induction. We confirm that quantitative changes mainly concern proteins involved in cell structure and motility. Furthermore, we describe the possible involvement of the asymmetric dimethylarginine pathway in the BBB phenotype re-induction process and we discuss asymmetric dimethylarginine's potential role in regulating endothelial function (in addition to its role as a by-product of protein modification). Our results also suggest that the intracellular redox potential is lower in the in vitro brain capillary endothelial cells displaying re-induced BBB functions than in cells with limited BBB functions