A. Flores-Rosas

Fine adjustment of cavity loss by Sagnac loop for a dual wavelength generation

We experimentally demonstrate a fine adjustment of cavity loss by Sagnac loop for a dual wave-length generation. The single or dual wavelengths are obtained by controlling the losses on both cavities through a fiber optical loop mirror (FOLM). Wavelength separation on the dual laser is 0.98 nm. The dual or single wavelength is obtained by changes in temperature in the order of 10−1°C around the maximum in the FOLM. Also, we investigate energy fluctuations on signal level saturation effect in the cavity through different pumping power that act on the EDF, where we note that from the 60-mW pumping begins to generate dual-wavelength and 80-mW stabilizes.

Theoretical and experimental analysis of tunable Sagnac high-birefringence loop filter for dual-wavelength laser application

We present detailed investigations of the spectral dependencies of the transmission of a fiber optical loop mirror (FOLM) consisting of a coupler with output ports spliced at arbitrary angles to a high-birefringence (Hi-Bi) fiber. The application for dual-wavelength lasers is discussed. For this aim, the spectral dependence of the reflection is tuned by the temperature of the Hi-Bi fiber that allows a fine adjustment of the cavity loss for generated wavelengths. The ratio between maximum and minimum reflection can be adjusted by the twist angle of the fiber at the splices, which also provides useful possibilities for the adjustment of cavity losses. We used the twist and temperature variation of the Hi-Bi fiber to change the operation from single wavelength to stable dual-wavelength generation with either equal or unequal powers of wavelengths.

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

We propose and compare with experimental data a two-stage model of supercontinuum formation in a fiber for nanosecond-long pulse with intensities in 10W range. As a result of the first stage, the sea of solitons is formed. The second stage is spectrum modification because of Raman interaction.

Tunable dual-wavelength actively Q-switched Er/Yb double-clad fiber laser

We demonstrate experimentally a dual-wavelength tunable actively Q-switched fiber laser using 3 m of Er3+/Yb3+ co-doped fiber as the gain medium. For wavelength tuning we used a tunable Hi-Bi FBG having two reflection wavelengths separated by 0.4 nm. The laser emits a dual-wavelength signal that is tunable in a range of 11.8 nm. Laser operation can be switched between single and double wavelength emission. The laser operates at repetition rates from 30 to 110 kHz with pulse durations of 280 ns and pulse energies near 0.5 μJ.

The use of NOLM for investigations of initial development of supercontinuum in fibers with anomalous dispersion

We performed a numerical study of the transmission through a nonlinear optical loop mirror (NOLM) of a sequence of solitons generated at the initial stage of the supercontinuum (SC) generation. We found that the NOLM exhibits a selective transmission that critically dependents on the amplitude of the input solitons and on the NOLM loop length. The results demonstrate that by properly selecting these parameters the NOLM behaves as an optically controlled switch that allows the transmission of solitons with similar amplitude and width. The results obtained by employing this method are reasonably good and can be used to analyze the soliton formation at the initial stage of SC generation.

Optimization of the two-stage single-pump erbium-doped fiber amplifier with high amplification for low frequency nanoscale pulses

We report the two-stage single-pump configuration of an erbium-doped fiber amplifier, in which a Sagnac interferometer is introduced to reduce the most important contribution of amplified spontaneous emission (ASE) noise, providing significant improvement on the amplifier performance. A Sagnac interferometer, made from a high-birefringence fiber loop, is included between the first and second stages. It is designed to provide transmittance with a period of 46 nm that allows us to adjust the minimum transmission around 1530 nm (peak of ASE noise) and maximum transmission at 1550 nm (signal wavelength). For optimizing the configuration, we measure the erbium-doped fiber parameters and simulate the amplification of the signal along the fiber. In the experiment, a significant absorption coefficient for pump and signal is found. The absorption looks to be too strong for the background absorption, and we suppose that it may be caused at least partly by excited-state absorption (ESA). Including the absorption coefficient allows very good correspondence between simulation and experiment. Experimental results show that with a simple configuration, we obtain up to 53-dB amplification with only 73 mW of pump power.

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.

Experimental investigation of the extraction of solitons at the initial stage of the soliton formation process

We demonstrate the extraction of a single soliton from a bunch of solitons generated by the pulse breakup effect. The bunch of solitons was generated in a 500-m fiber pumped by 25-ps pulses. For the extraction of single soliton from the bunch we use a nonlinear optical loop mirror (NOLM). At its output we detected a pulse with full width at half-maximum (FWHM) of 0.99 ps whose autocorrelation trace corresponds to that of a soliton. Our results demonstrate that the suggested method can be useful for soliton generation, and also for investigations of the initial stage of the soliton formation process.

Soliton extraction from a bunch of solitons resulting from pulse breakup by using a nonlinear optical loop mirror

We numerically investigated the transmission of a bunch of solitons resulting from the breakup of pulses with duration of several tens of picoseconds (ps) through a nonlinear optical loop mirror (NOLM) and found that under some conditions an individual soliton can be extracted. The NOLM selectivity can be adjusted by the amplification of the bunch of solitons before it is launched into the NOLM. The results demonstrate that an appropriate choice of the amplification and of the NOLM loop length makes it possible to extract one fundamental soliton and to tune the soliton duration. For a particular case of 20 ps input pulses, the duration of the extracted soliton was tuned in the range between 0.23 and 0.61 ps. We believe that the suggested method can be useful for producing solitons with desirable duration.

Polarization properties of vector solitons generated by modulation instability in a fiber with circular birefringence

Abstract. We analyzed the two coupled propagation equations in a circularly birefringent fiber. We found that the difference between perpendicular and parallel Raman gain results in energy transform from a slow to fast circularly polarized component. We have shown this effect analytically and by a numerical simulation. We analyzed and measured the polarization of solitons generated by modulation instability and we found that polarization ellipticity of solitons is distributed randomly; however, the ellipticity of polarization is close to the polarization of the input pulse and always is shifted toward the circular polarization. Therefore, if a circularly polarized pulse is launched at the fiber input then the produced solitons are also circularly polarized. In the experiment, we used SMF-28 twisted fiber by 6  turns/m; the fiber twist mitigated the random linear birefringence, and the fiber was pumped by 1-ns pulse. We have found that circular polarization of the pump pulse in the twisted fiber produces circularly polarized solitons with a high grade of polarization while in the fiber without twist the soliton polarization was random.