Autor: EVGENY KUZIN

High gain erbium-doped fiber amplifier for the investigation of nonlinear processes in fibers

EVGENY KUZIN (2008)

In this work we present a novel design of an optical amplifier with high gain elaborated from erbium-doped fiber (EDF). Its purpose is the amplification of low power pulses from laser diodes. The high power of the output pulses allows the investigation of nonlinear processes in optical fibers. The optical amplifier consists of two stages. The first stage uses a reflective configuration where a signal is amplified twice in the same EDF. The fiber Bragg grating (FBG) was the main element to reflect the signal. The second stage works as a high power amplifier. The input pulse has duration in the range of 1 to 50 ns, with wavelength equal to 1549.1 nm. With input pulse power of 1.5 mW, the amplifier provides 70 W in the output pulse. The gain obtained by the amplifier was 47 dB.

Artículo

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

Large signal-to-noise-ratio enhancement of ultrashort pulsed optical signals using a power-symmetric nonlinear optical loop mirror with output polarisation selection

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2009)

A numerical study of a fibre-based scheme for the regeneration of ultrashort-pulsed optical signals is presented. The setup is made of a power-symmetric Nonlinear Optical Loop Mirror (NOLM) followed by a polariser. The NOLM operates through nonlinear polarisation rotation, and includes twisted, anomalousdispersion fibre and a quarter-wave retarder. When the orientations of the linear input polarisation and of the output polariser are properly adjusted, the output energy characteristic flattens at high power, a property that can be used to eliminate large amplitude fluctuations on the logical ones of an optical signal. When the input pulse parameters closely match those of fundamental solitons or of stable elliptically polarised solitary waves, a wide and flat plateau is obtained, allowing the reduction of ∼30% amplitude fluctuations to less than 1%. Very large amplitude fluctuations beyond 50% can also be reduced down to a few %. Although the output pulses are slightly chirped, they are free of pedestal, thanks to the zero low-power transmission of the NOLM, which also allows the simultaneous regeneration of logical zeros. We believe that this setup will be useful for the regeneration of highly degraded signals in future ultrafast transmission networks.

Artículo

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

Optical pulse compression and amplitude noise reduction using a non-linear optical loop mirror including a distributed Gires–Tournois etalon

BALDEMAR IBARRA ESCAMILLA EVGENY KUZIN (2010)

We propose and analyse numerically a novel dispersion-imbalanced non-linear optical loop mirror (NOLM) scheme allowing simultaneous compression and amplitude noise reduction of chirped ultrashort-pulsed signals. An all-fibre distributed Gires–Tournois etalon (DGTE) made of two uniform fibre Bragg gratings is inserted asymmetrically in the loop, and is used both to dispersion imbalance the NOLM and to compress the pulses. The results show that the output pulses are accompanied by side lobes, which originate from the no-uniformity of the DGTE dispersion spectrum. We analyse the formation of these side lobes and show that, in the case of highly chirped input pulses, side lobes are strongly reduced by the NOLM architecture. In this case, the device operates well even when the signal optical spectrum extends over an entire free spectral range of the DGTE. We believe that this work will be useful for the design of all-optical regeneration schemes for highly chirped data streams in optical transmission systems.

Artículo

Non-linear optical loop mirror Gires–Tournois interferometer Fibre Bragg grating CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

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.

Artículo

Fiber laser Optical pulses 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.

Artículo

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.

Artículo

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.

Artículo

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

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.

Artículo

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.

Artículo

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.

Artículo

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