M. Bello-Jiménez

Initial development of supercontinuum in fibers with anomalous dispersion pumped by nanosecond-long pulses

We propose a simple two-stage model of supercontinuum formation for nanosecond-long pulse. First the sea of solitons is formed, then the spectrum is broadened by Raman interaction. We found a good correspondence with experiments.

Improved All-Fiber Acousto-Optic Tunable Bandpass Filter

An all-fiber acousto-optic tunable bandpass filter based on a 1.185-mm long coreless core mode blocker is reported. Experimental results demonstrate a minimal insertion loss of 1.2 dB at the optical resonant wavelength of 1527.7 nm with 3-dB optical bandwidth of 0.83 nm. The optimization of the device takes into account the attenuation of the acoustic wave and leads to an asymmetric configuration in which the coupling section is shorter than the recoupling part. Under the effect of a standing flexural wave the device can be operated as a bandpass modulator. The device exhibits a maximum modulation depth of 28%, 4 dB of insertion loss and 0.97 nm of optical bandwidth at 4.774 MHz.

Complex dynamics of a fiber laser in non-stationary pulsed operation.

Conventional mode locking is characterized by the generation of a stable train of optical pulses. Even in the noise-like pulsing regime of fiber lasers, sometimes described as partial mode locking, a periodic train of waveforms is still generated. In this work we study the dynamics of a figure-eight fiber laser away from the stable noise-like pulsing regime. By analyzing sequences of time-domain measurements performed with ns resolution, we reveal a wide range of puzzling dynamics, in which sub-structures emerge and drift away from the main bunch, decay or grow in a step-like manner, before vanishing abruptly. In some cases, sub-packets also concentrate in the central part of the period, forming one or multiple wide clouds that merge or split over time scales of seconds or minutes. Spontaneous transitions between these multiple states occur in a non-periodic manner, so that no quasi-stationary behavior is found over long time scales. These results provide a dramatic illustration of the extremely rich dynamics taking place in fiber lasers at the frontier of mode locking.

Two-stage single-pump Er-doped fiber amplifier with 55-dB amplification ns-long pulses

In this paper, we theoretically and experimentally investigated a two-stage erbium-doped fiber amplifier (EDFA) with a single-pump laser diode pumped at 980 nm in which a Sagnac interferometer filter is introduced to reduce amplified spontaneous emission (ASE) providing significant improvement on the amplifier performance. The erbium-doped fiber (EDF) parameters were measured in order to optimize parameters such as pump power, EDF length, ASE noise and signal gain. The Sagnac interferometer filter was designed to provide a periodic transmittance of 46 nm that allows by temperature to adjust the minimum transmission at 1530 nm (peak of the ASE noise) and maximum transmission at 1550 nm (signal wavelength). Experimental results show that with a simple configuration we obtained up to 53-dB amplification with only 75 mW of pump power, which can be enhanced easily by 3 dB providing total amplification up to more than 55 dB.

Experimental investigation of pedestal suppression in a figure-eight fiber laser by including a polarization asymmetrical NOLM

A polarization asymmetrical nonlinear optical loop mirror (NOLM) is investigated to perform pedestal-free optical pulses in a figure-eight laser (F8L). The results demonstrate that in the low-power regime the NOLM operates as a halfwave plate and the output polarization is orthogonal to the input one. However, at higher power level the polarization component parallel to the input appears, with a transmission that always begins from zero at low power, allowing the rejection of low-intensity components. Experimental results demonstrate that by employing this configuration we can obtain a contrast between the peak and continuous background higher that 40 dB.

Fine adjustment of cavity loss by fiber optical loop mirror for dual-wavelength laser

We report numerically and experimentally analysis of optic fiber Sagnac interferometer and fine adjustment of cavity loss by the use of the FOLM with a hi-bi fiber in the loop. Changes in transmittance profile amplitude and wavelength shift are caused by the whirl effect in the connectors of a coupler with ports output connected to a birefringent fiber. Also the experimental demonstration of dual wavelength operation of a fiber laser through fine adjustment of cavity loss, using a Fiber Optical Loop Mirror (FOLM) with a high-birefringence fiber in the loop. The reflection and transmission of the FOLM presents a sinusoidal wavelength dependence which can be shifted by controlling the temperature of the hibi fiber. A temperature change of the hi-bi fiber by 0.1°C causes a measurable change in the ratio between the reflectance for the wavelengths R(λ1)/R(λ2). Using this adjustment be able to change the generation mode from single wavelength to stable dual wavelength generation with equal powers for λ1 and λ2 or to stable dual wavelength generation with unequal powers at λ1 and λ2. The change of the ratio between the FOLM reflection R(λ1)/R(λ2) allows the investigation of tolerance of dual wavelength generation on the ratio between cavity loss. Was found that for the switch from a single wavelength emission at λ1 to single wavelength emission at λ2 the ratio R(λ1)/R(λ2) has to be changed by the order of magnitude of 10-2. This value shows the tolerance of the dual wavelength laser to the cavity loss adjustment.

Extraction of a single soliton from a set of solitons by the use of a nonlinear optical loop mirror

We investigated numerically the transmission of a set of solitons through a nonlinear optical loop mirror (NOLM) and found that under some conditions a single soliton can be extracted. We analyzed the evolution of relatively long (20-50 ps) and no very strong (10 W) pulses. The results show that the input pulse duration and the amplification of the solitons resulting from pulse breakup play important role to extract the highest quality pulse. The transmitted pulses correspond to fundamental solitons with subpicosecond durations. We believe that the proposed method can be useful for the study of nonlinear phenomena in optical fibers.

Pulse Shaping of ns-Scale Pulses Using Modulation Instability

The pulses form DFB laser amplified to 1-50 W were launched to the fiber. MI side lobs were then filtered. Resulting wave form shows to be more squared with substantially reduced relaxation oscillation peak.