Author: BALDEMAR IBARRA ESCAMILLA

An all fiber based Talbot self-imaging mirror device for phase-locking of a multi-fiber laser

Baldemar Ibarra Escamilla (2012)

By propagating beamlets from a periodically placed array of single-mode fiber amplifiers in a large mode-are (LMA) fiber, we find that a self-image of the initial beamlets is formed at certain distances in the LMA fiber. A Talbot mirror fiber device (TMFD) based on this property is proposed for phase-locking of a multi-fiber laser. For this laser system, we investigate how the LMA fiber length variation; the fiber amplifier phase variation, amplitude variation, and displacement affect the self-image qualities and the coupling efficiency.

Article

Talbot and self-imaging effects Fiber laser Phase-locking CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Analysis of a polarisation-maintaining NOLM switch for OTDM applications

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2008)

We propose a polarisation-maintaining NOLM switch design to be used as optical regenerator or wavelength converter in dense optical time-division multiplexed (OTDM) systems. The Sagnac loop is made of a piece of high birefringence fibre which is cut and crossspliced in the middle. If pump and probe polarisations are linear and aligned in the co-propagating direction, the cross-splice ensures that the counter-propagating probe beam will be orthogonal to the pump, so that the parasitic cross-phase modulation between counter-propagating beams is minimised. This architecture also allows easy control of the optical phase bias, through squeezing a short section of the fibre, without any other modification of the setup. The performances of the proposed architecture are studied analytically and numerically, and compared with those of conventional schemes. It appears that, although the proposed setup reduces the interaction between counter-propagating beams only by a factor 3, it yields an extinction ratio improvement of a factor 10 or higher in comparison with conventional schemes. If there is substantial walkoff between pump and probe, a 10-fold reduction of the relative intensity noise of the emerging signal is also obtained when the mark ratio of the incoming data is variable.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA OPTICA FÍSICA

Step-like all-optical decision function using nonlinear polarisation rotation in a nonlinear optical loop mirror and in a subsequent fibre section with output polarisation selection

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2009)

We propose and study numerically a fibre-based scheme designed to generate a step-like optical decisión function for ultrafast data processing applications. The setup includes two main sections disposed in series: a Nonlinear Optical Loop Mirror with an output polariser on the one hand, and a circularly birefringent fibre span with a quarter wave retarder at the input and a polariser at the output on the other hand. Both sections operate through nonlinear polarisation rotation, and the switching characteristic is controlled through the light ellipticity, which can be adjusted by setting properly the orientation of the input polarisation, and by rotating the wave retarder and the two polarisers. For proper adjustment of these four parameters, a step-like optical decision function with ∼10 dB/dB steepness is predicted. In the frame of all-optical regeneration, the setup allows eliminating ∼76% peak-to-peak amplitude fluctuations on the marks and ∼30% relative power on the spaces. We believe that this architecture should be considered for the design of ultrafast transmission networks and in the frame of all-optical computing applications.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA OPTICA NO LINEAL

Large amplitude noise reduction in ultrashort pulse trains using a power-symmetric nonlinear optical loop mirror

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2009)

We analyse numerically the capabilities of a power-symmetric nonlinear optical loop mirror (NOLM) in the ultrashort pulse regime for high-quality amplitude regeneration of an optical signal. The device, which operates through nonlinear polarisation rotation, includes twisted, anomalous-dispersion fibre and a quarter-wave retarder. For particular adjustments of the retarder orientation, and a circularly polarised input beam, the output energy characteristic flattens near the switching energy, a property that can be used to eliminate large amplitude fluctuations in an optical signal. The group velocity mismatch between polarisation components introduced by twist is mitigated by the interplay between anomalous dispersion and the nonlinear Kerr effect, although strong twist should be avoided as it still introduces substantial pulse distortion. Contrary to other designs, where a plateau characteristic requires a large power imbalance between the counter-propagating beams, both pulses in the present scheme can be simultaneously close to fundamental solitons, which allows a substantial widening of the plateau for particular pulse parameters. Good quality, nearly transform-limited pulses are obtained in this case at the NOLM output. The device is applicable for the regeneration of ultrafast data streams in which the signal-to-noise ratio is severely deteriorated.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA OPTICA NO LINEAL

Adjustable noiselike pulses from a figure-eight fiber laser

Baldemar Ibarra Escamilla EVGENY KUZIN (2011)

We propose and study experimentally and numerically a passively mode-locked figure-eight fiber laser scheme generating noiselike optical pulses, or subns wave packets with a fine inner structure of subps pulses presenting random amplitudes and durations. The particular design of the nonlinear optical loop mirror (NOLM) used in this laser, relying on nonlinear polarization rotation, allows adjusting the switching power through input polarization control. Experimental results show stable pulsed operation over a limited range of the NOLM input polarization angle. Interestingly, the spectral and temporal characteristics of these pulses are observed to be widely variable over that range. In particular, the spectral width varies from 16 to 52nm and this spectral variation is associated with an inverse evolution in the durations of the bunch and of the inner ultrashort pulses. Simulation results are in good agreement with the experiment. They confirm the strong dependence of the pulse properties on the value of the NOLM switching power, although NOLM switching is not alone responsible for the appearance of the noiselike pulsing mode.

Article

Fiber laser Optical pulses CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Optical pulse shaping at moderate power using a twisted-fibre NOLM with single output polarisation selection

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2008)

We demonstrate theoretically and experimentally that efficient signal shaping operation can be obtained at moderate power by using the transmission characteristic of a power-symmetric nonlinear optical loop mirror (NOLM) including highly twisted fibre and operating through nonlinear polarisation rotation, when the circular polarisation state orthogonal to the input polarisation is selected at the NOLM output. By adjusting the angle of the quarter-wave retarder inserted in the loop, the phase bias of the transfer characteristic

can be adjusted precisely to enable proper signal shaping for moderate values of input power, remaining well below switching power. The tolerance of the procedure to deviations of the input polarisation from the ideal circular case is investigated numerically. We demonstrate experimentally the capabilities of this setup for both power equalisation and extinction ratio enhancement. Finally, we show that this setup is also useful to shape ultrashort optical pulses from the relaxation oscillations of a DFB semiconductor laser. In comparison with other NOLM-based techniques, the proposed approach allows to reduce by a factor of 8–10 the peak power required for pulse shaping, for the same fibre length and Kerr coefficient.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA FIBRAS ÓPTICAS

High-energy pulses from a figure 8 fiber laser with normal net dispersion¹

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2009)

In this paper we show numerically that high-energy pulses can be obtained with a figure-eight Erbium-doped fiber laser with large normal net dispersion, and in which an anomalous-dispersion Nonlinear Optical Loop Mirror (NOLM) is used as the effective saturable absorber. One advantage of this configuration over the ring cavity is the possibility to adjust the length of the NOLM loop to avoid overdriving the saturable absorber. The ring section of the laser includes a bandpass filter to balance the combined effects of Kerr nonlinearity and normal dispersion. Strict polarization control is performed in the NOLM as well as in the ring section of the laser. The NOLM is a power-symmetric scheme whose switching relies on nonlinear polarization rotation. This architecture allows a precise control of the low-power NOLM transmission through the orientation of a quarter-wave retarder, whose adjustment is shown to be critical for stable pulsed operation. Pulse formation appears to depend critically on the filter width. If it is wide enough, ps pulses with a large positive linear chirp are produced. After dechirping outside the laser, nearly transform-limited pulses with durations down to 240 fs, energies up to 10 nJ and peak powers beyond 40 kW are predicted.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA LÁSERES

Generation of long broadband pulses with a figure-eight fiber laser¹

Baldemar Ibarra Escamilla EVGENY KUZIN (2011)

In this paper we performed the experimental and numerical study of a passively mode-locked fiber laser that generates packets of sub-picosecond pulses instead of individual pulses. The proposed configuration is a figure-eight fiber laser scheme, which includes a Nonlinear Optical Loop Mirror with polarization asymmetry inserted into a ring cavity. No experimental evidence of self-starting mode locking operation of the laser was observed; however, for proper adjustments of the wave retarders included in the setup, a mechanical stimulation triggers the onset of mode locking. The autocorrelation of the generated pulses shows a narrow sub-picosecond peak riding a large sub-nanosecond pedestal whose intensity is half that of the peak, and the optical spectrum is smooth and wide. We show that contrary to conventional ultrashort pulses, these pulses do not vanish rapidly after propagation through a long dispersive fiber, which makes then attractive for super-continuum generation as well as for applications in metrology. Finally, we study the pulse formation in the laser and present arguments based on experimental data and numerical simulations that the observed pulses are actually sets of a large number of solitons.

Article

Fiber laser Polarization asymmetry CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Generation of high-energy pulses from an all-normal-dispersion figure-8 fiber laser¹

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2010)

We propose and study numerically an all-normal-dispersion Ytterbium-doped figure-eight fiber laser scheme for generation of high-energy pulses. The monotonous pulse stretching that takes place in the fiber under the combined actions of normal dispersion and nonlinear Kerr effect is compensated by the amplitude modulation effect of a bandpass filter inserted in the ring section of the laser. The Nonlinear Optical Loop Mirror (NOLM) also contributes to shorten the pulses. An output coupler with a large output coupling ratio is inserted at the amplifier output in order to extract the maximal energy from the laser. A short segment of Ytterbium-doped fiber compensates for the losses. Stable single-pulse operation is predicted over a wide range of values of the laser parameters. If the laser parameters (ring and NOLM length, dispersion, filter bandwidth, output coupling ratio) are optimized, pulses with several tens of nanojoules energy are readily obtained, with picosecond duration and a large positive chirp which is linear near the peak. If small-signal gain is large enough, the use of very large output coupling ratios opens the way to pulse energies close to 100 nJ and, after dechirping outside the laser, to durations of ~50 fs and peak powers of 1 MW.

Article

Generation of High-Energy Nonlinear optical CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Tuneable sagnac comb filter including two wave retarders

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2010)

In this paper we study theoretically and experimentally a wavelength-tuneable Sagnac birefringence filter. The device is a Sagnac interferometer including a symmetric fibre coupler and a length of high birefringence fibre in the loop. A wave retarder is inserted at each end of the birefringent fibre for absolute wavelength tuning. We show theoretically that wavelength tuning through wave plate orientation ensuring constant amplitude of the filtering function is possible only if a minimum of two wave retarders are included in the setup. The position of the transmission peaks then varies linearly with the angle of one of the retarders and can be adjusted over one entire channel spacing. This happens only only when a quarter-wave retarder and a half-wave retarder are used, if the former is oriented at 45° with respect to the fibre birefringence axes, while the orientation of the latter serves as the adjustment parameter. The theoretical predictions are confirmed by the experimental results.

Article

Sagnac interferometer Fibre-optic devices Tunable filters CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA