Juan Carlos Hernández-García

Adjustable noiselike pulses from a figure-eight fiber laser

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 52u2009nm 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.

Supercontinuum generation in a standard fiber pumped by noise-like pulses from a figure-eight fiber laser

We report the experimental study of broadband spectrum generation in a piece of standard fiber (SMF-28) using as the pump a train of noise-like pulses, or sub-nanosecond packets of sub-ps pulses with randomly varying amplitudes. The pulses are generated by an erbium-doped figure-eight fiber laser, and present a wide (∼50 nm) optical spectrum, which represents a significant advantage to seed the generation of new frequencies. Another advantage of the pulses is their relatively large energy, as they are made up of a large number of ultrashort pulses. After amplification with an Erbium Doped Fiber Amplifier (EDFA), the pulses were injected in a 0.75 km length of SMF-28 fiber. We obtained experimentally at the end of the fiber an output signal spectrum extending from 1530 nm to at least 1750 nm (the upper limit of the spectrum analyzer) for pump pulses with an average power of 20.4 mW, corresponding to a few kilowatts peak power. The spectral broadening is due to Raman self-frequency shift (SFS). It is noteworthy that the spectrum of the newly created frequencies was extremely uniform over the range of measurement. Considering that the Raman shift is directly related to the pump pulse duration, spectral flatness is a direct consequence of the random distribution of amplitudes and durations of the pulses in the packet. Finally, the results show the capabilities of noise-like pulses from a fiber laser for applications in supercontinuum generation based on nonlinear phenomena such as Raman SFS.

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

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.

Long Period Fiber Grating Produced by Arc Discharges

Fiber Gratings are found among the most popular devices widely used in both, optical communications and optical fiber sensing. Within optical communication networks, optical fiber-based devices perform critical operations such as coupling/splitting, wavelengthselective filtering, and optical switching (Han, Y. G. et al., 2004; An H. et al., 2004; Eggleton B. J. et al., 1997). In the field of optical sensing, optical fiber sensors, with unique advantages such as immunity to electromagnetic interference, high sensitivity, resistance to corrosion, and high temperature survivability, are widely used to measure various physical variables such as stress, temperature, pressure, refractive index, etc. and chemical parameters (Udd, E. 1991).

Multiple continuous-wave and pulsed modes of a figure-of-eight fibre laser

We study experimentally a figure-of-eight fibre laser including a polarization-imbalanced nonlinear optical loop mirror and a Mach–Zehnder optical filter formed by two fibre tapers placed in series. Depending on the adjustments of two wave retarders included in the setup, different modes of operation of the laser are found. In continuous-wave mode, tunable single-wavelength operation as well as multiwavelength lasing are observed. For some adjustments, self-pulsing also takes place, although the pulses are very unstable. Finally, for some adjustments a mechanical stimulation (a kick) leads to the onset of passive mode locking. Measurements reveal that the mode-locked pulses actually are noise-like pulses. Both stable fundamental mode locking and second-harmonic mode locking with particular dynamics were obtained. In this work, we analyse how simple wave plate adjustments can lead to such a variety of operational modes of the fibre laser.

Dual-wavelength operation of a figure-eight fiber laser

We study numerically an erbium-doped figure-eight fiber laser including a double-band-pass optical filter for dual-wavelength pulse generation. Simulations are performed for several values of the filter band-width and wavelength separation between the transmission windows. The results show that dual-wavelength mode-locking is obtained in most cases, with a balanced energy distribution between wavelengths. Due to cavity dispersion, the pulses at each wavelength are asynchronous for a large wavelength separation, whereas they are synchronous for closely spaced wavelengths, as in this case cross-phase modulation is able to compensate for the dispersion-induced walkoff. In the asynchronous case, dual-wavelength operation is favored by the filter loss, whereas in the synchronous case it is favored by the saturable absorber action of the nonlinear optical loop mirror. Simulations also show that, thanks to those stabilization mechanisms, dual-wave-length pulsed operation does not require precise cavity loss equalization between the two oscillating wave-lengths.

The polarization effects of the pumping source of a ring tunable wavelength laser Er-doped fiber

The analysis of polarization evolution in a tunable fiber laser in a ring configuration is presented, an interferometer was used to tune the laser and was manufactured with thin-core fiber (Thin-Core Fiber, TCF). The interferometer was achieved by splicing a segment of thin-core fiber (Thin-Core Fiber, TCF) between two segments of single-mode fiber SMF-28 (Single-Mode Fiber). Single and double and triple line emissions were obtained by means of the angular micrometric deflection in the TCFMI (Thin-Core Fiber Modal Interferometer) interferometer section, as well as depending on the position of the polarization controller plates (PC1 and PC2). Also, a uniform tuning was achieved, depending on the polarization state of the pumping source and the position of the plates of the second polarization controller (PC2), which started at 1534.70265 nm and moved to the left side to 1531.65142 nm and the evolution of the polarization state in this tuning range was observed. A tuning range of 1527.01738 to 1553.66363 nm was also achieved by means of the angular micrometric deflection in the TCFMI interferometer section.