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ABSTRACT: In-fiber mode engineering based on the combination of Bragg and long-period gratings (LPGs) permits the implementation of noninterferometric transmission filters with narrow passbands using standard single-mode fiber. The design of the bandpass filter is based on the coupling between propagating and counterpropagating cladding modes in two fiber Bragg gratings. A LPG located between the Bragg gratings transfers power from the input fundamental mode to a specific cladding mode and recouples the filtered signal to the output fundamental mode. The filter produces a series of narrow passbands of about 30 pm linewidth with a maximum transmittance above 60%, 20 dB isolation, and passband separation of about 1 nm, each corresponding to the contribution of a different cladding mode.
Optics Letters 10/2012; 37(20):4314-6. · 3.40 Impact Factor
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ABSTRACT: We show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical
fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off,
the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were
successfully obtained at repetition rates in the range 1–10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength
of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at
7 kHz repetition rate.
Laser Physics 05/2012; 21(9):1650-1655. · 3.61 Impact Factor
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ABSTRACT: We report an experimental study of an actively mode-locked fiber ring laser based on the development of an efficient in-fiber
amplitude modulator. Intermodal coupling induced by standing flexural acoustic waves permits the implementation of broad bandwidth
(1.5nm), high modulation depth (72%), low-insertion-loss (0.75dB), in-fiber amplitude modulators, operating in the MHz frequency
range. The experimental characterization of the laser as a function of the radio frequency voltage that controls the modulator,
the length of the active fiber, and the optical bandwidth of an intracavity filter implemented with a fiber Bragg grating
has led to an improved performance of the Erbium-doped fiber laser: optical pulses of 34-ps temporal width, 1.4-W peak power,
and 4.75-MHz repetition rate.
Applied Physics B 04/2012; 105(2):269-276. · 2.19 Impact Factor
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ABSTRACT: We report an experimental study of an actively mode-locked erbium-doped all-fiber laser, based on a standing-wave acoustically-induced
superlattice modulation. Our experiments involve the characterization of the laser as a function of the active fiber length,
and with different types of delay line fibers. The effect of the modulation on the laser performance was also investigated.
Narrower pulses were obtained at higher modulation depths, normal dispersion, and shorter lengths of active fiber. Optical
pulses of 160mW peak power and 630ps temporal width were obtained at 9MHz repetition rate.
Applied Physics B 04/2012; 99(1):95-99. · 2.19 Impact Factor
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ABSTRACT: We report experimental results on supercontinuum generation in a highly Ge-doped core Y-shaped microstructured optical fiber
using pump pulses of 9 ns duration at 1064 nm. The fiber is easy to fabricate due to its simple structure and shows good compatibility
with standard fiber. The generation of nonlinear effects takes advantage of the large nonlinear refractive index and Raman
gain of the Ge-doped core, as well as the air hole structure that surrounds the core. Although the fiber was pumped in normal
dispersion and relatively far from the zero dispersion wavelength, flat and smooth supercontinuum in the fundamental mode
from 550 nm to beyond 1750 nm was generated with a rather moderate value of fiber length and pump peak power product of 13
kW⋅m.
Applied Physics B 04/2012; 98(2):371-376. · 2.19 Impact Factor
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ABSTRACT: We propose a simple technique to measure in the time domain the magnitude of frequency chirp of high-speed temporal complex
waveforms. The technique relies in the properties of three time-domain chirp-sensitive operations: the Hilbert transform,
the integration, and the differentiation, all of them analyzed in its integer and fractional counterpart. The implementation
of these operations through fiber Bragg gratings is also discussed. We numerically prove the viability of this technique.
KeywordsChirp–Fiber optics–Fiber Bragg grating
Optical and Quantum Electronics 04/2012; 42(2):97-108. · 0.82 Impact Factor
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ABSTRACT: An experimental study of the effects of an auxiliary 976 nm pump signal on the four-wave mixing parametric bands generated with a 1064 nm pump in a normal dispersion Er-doped photonic crystal fiber is presented. The four-wave mixing signal and idler bands shift to shorter and longer wavelengths, respectively, with increasing 976 nm pump power. It is shown that the wavelength-dependent resonant refractive index change in the erbium-doped core under 976 nm pumping is at the origin of the effect.
Optics Letters 04/2012; 37(7):1226-8. · 3.40 Impact Factor
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ABSTRACT: We show that whispering-gallery modes (WGMs) in optical microresonators can be excited and detected using a fused-tapered fiber tip (FTFT). The fabrication of FTFTs is simple and inexpensive; they are robust and allow the excitation and interrogation of the resonances with a single fiber. Excitation of high-Q WGMs in silica microcylinders and microspheres is demonstrated.
Optics Letters 09/2011; 36(17):3452-4. · 3.40 Impact Factor
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ABSTRACT: A technique for the development of low-cost and high-sensitivity photonic biosensing devices is proposed and experimentally demonstrated. In this technique, a photonic bandgap structure is used as transducer, but its readout is performed by simply using a broadband source, an optical filter, and a power meter, without the need of obtaining the transmission spectrum of the structure; thus, a really low-cost system and real-time results are achieved. Experimental results show that it is possible to detect very low refractive index variations, achieving a detection limit below 2×10(-6) refractive index units using this low-cost measuring technique.
Optics Letters 07/2011; 36(14):2707-9. · 3.40 Impact Factor
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ABSTRACT: We present a fiber laser made in a single piece of conventional doped-core fiber that operates by combined feedback of the fundamental core mode LP((0,1)) and the high-order cladding mode LP((0,10)). The laser is an all-fiber structure that uses two fiber Bragg gratings and a long-period grating to select the modes circulating in the cavity; the laser emits at the coupling wavelength between the core mode LP((0,1)) and the counterpropagating cladding mode LP((0,10)) in the Bragg gratings. This work demonstrates the feasibility of high-order mode fiber lasers assisted by long-period gratings.
Optics Letters 05/2011; 36(10):1839-41. · 3.40 Impact Factor
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ABSTRACT: We present an experimental demonstration of energy transfer between counterpropagating cladding modes in a fiber Bragg grating (FBG). A strong FBG written in a standard photosensitive optical fiber is illuminated with a single cladding mode, and the power transferred between the forward propagating cladding mode and different backward propagating cladding modes is measured by using two auxiliary long period gratings. Resonances between cladding modes having 30 pm bandwidth and 8 dB rejection have been observed.
Optics Letters 04/2011; 36(8):1518-20. · 3.40 Impact Factor
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ABSTRACT: In-fiber efficient light modulation using two concatenated long-period gratings (TCLPG), written in single-mode fiber, is reported. The device is compressed in the middle of both gratings against a corrugated surface, with a piezoelectric, producing a transfer of energy between cladding modes which results in modulated light transmission. The TCLPG operates at 1542 nm, with a bandwidth of 29 nm and an insertion loss of 0.3 dB. The modulation depth is 20 dB and the rise time is 7.5 ms at a repetition rate of kilohertz.
IEEE Photonics Technology Letters 03/2011; · 2.19 Impact Factor
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ABSTRACT: We have investigated the generation of supercontinuum in tapered Y-shaped fibers in the nanosecond pump regime. This fiber used to fabricate the tapers has, in addition, a Ge-doped core which enhances the nonlinearity of the material and the Raman gain. The fiber was pumped at 1064 nm in the ns pump regime (0.6 ns pulses and up to 3.2 kW peak power). The taper had a uniform waist of 0.9 μm diameter and 130 mm length, and the adiabatic transitions were 110 mm long. A flat spectrum spanning from 420 nm to 1870 nm was obtained using a single tapered fiber.
Journal of Physics Conference Series 02/2011; 274(1):012016.
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ABSTRACT: We present a sensing technique based on using photonic bandgap structures where only the output power is monitored, without the need of tunable sources or spectrum analyzers, thus providing a real-time and low-cost system.
01/2011;
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ABSTRACT: A novel tunable photonic microwave single bandpass filter based on the optical resonance originated by a local phase shift introduced in the periodic structure of a fiber Bragg grating is proposed. Dynamic control of the phase shift is obtained employing a piezoelectric transducer in order to stretch the grating, thus changing the resonance wavelength. A photonic microwave filter is obtained by using an optical single-sideband modulation. Experimental results are provided in order to prove the concept.
IEEE Photonics Technology Letters 11/2010; · 2.19 Impact Factor
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ABSTRACT: We report an actively mode-locked fiber ring laser. A simple and low-insertion-loss acousto-optic modulator driven by standing flexural waves, which couples core-to-cladding modes in a standard single-mode optical fiber, is used as an active mechanism for mode locking. Among the remarkable features of the modulator, we mention its high modulation depth (72%), broad bandwidth (187 GHz), easy tunability in the optical wavelength, and low insertion losses (0.7 dB). The narrowest optical pulses obtained were of 95 ps time width, 21 mW peak power, repetition rate of 4.758 MHz, and 110 mW of pump power.
Optics Letters 11/2010; 35(22):3781-3. · 3.40 Impact Factor
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ABSTRACT: The cutoff properties of the fundamental mode of liquid filled Ge-doped microstructured fiber can be exploited in a novel set of wavelength encoded sensor applications. A number of temperature, strain and vibration sensors have been implemented using a Ge-doped core Y-shaped microstructured fiber. The temperature sensitivity of the cutoff wavelength is 25 nm/°C, more than two orders of magnitude higher than the values reported for fiber Bragg gratings. Similarly, the strain sensitivity is 16.8 pm/μ∈, about one order of magnitude higher than a fiber Bragg grating. Amplitude interrogation of the sensor heads can be implemented in rather easy configurations using a light emitting diode or a laser diode, without requiring an accurate selection of the laser wavelength. This permits, for example, the development of vibration sensors with fast time response, at least better than 0.1 ms.
IEEE Sensors Journal 08/2010; · 1.52 Impact Factor
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ABSTRACT: We report the generation of supercontinuum in a Ge-doped Y-shape tapered fiber pumped at 1064 nm in the ns pump regime. The taper was designed to have long taper transitions and a taper waist with a core diameter of 0.9 mum. The large air-filling fraction and diameter of the air-hole microstructure reduces the confinement loss at long wavelengths so, enabling the extension of the spectrum to longer wavelengths. Along the taper transition the zero-dispersion wavelength decreases as the diameter of the taper becomes smaller. The spectral components generated along the taper transition pump the taper waist, enhancing the generation of short wavelengths. A flat spectrum spanning from 420 nm to 1850 nm is reported.
Optics Express 07/2010; 18(14):14535-40. · 3.59 Impact Factor
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ABSTRACT: In this paper we present an actively switched fiber laser with an all-fiber long-period grating-based interferometer used as an intra-cavity loss modulator. The modulator consists of two equal long-period gratings written sequentially in the same piece of a double-clad optical fiber. One of the gratings is fixed onto a piezoceramic cylinder producing fast modulation of the interferometer transmission spectrum. The laser demonstrates a stable regime of pulsed emission at repetition rates in the range of tens of kHz.
Optics Communications 07/2010; 283(14):2892-2895. · 1.49 Impact Factor
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ABSTRACT: We present an optical fiber refractometer based on a Fabry-Perot interferometer defined by two fiber Bragg gratings and an intracavity long-period grating that makes the light confined in the resonator interact with the surrounding medium. The external refractive index is monitored by the resonant frequencies of the Fabry-Perot interferometer, which can be measured either in transmission or in reflection. In this first experiment, wavelength shifts measured with a resolution of 0.1 pm have allowed one to establish a refractive index detection limit of 2.1x10(-5).
Optics Letters 02/2010; 35(4):613-5. · 3.40 Impact Factor
