Evgueni A. Kuzin

We study numerically complex noise-like pulse dynamics in a passively mode-locked erbium-doped fiber laser. Wavelength-dependent gain dynamics is modeled as a combination of a three-level and a four-level system, which approximate the gain behavior in the 1530-nm and 1560-nm regions, respectively. The typical deformation of the erbium gain spectrum as it saturates is properly reproduced by this approach. Several puzzling noise-like pulse dynamics that were recently observed experimentally are qualitatively reproduced numerically, in particular slow quasi-periodic energy variations and the emergence and walkoff of wavelength-shifted radiation components. These results clearly reveal that gain dynamics is deeply involved in the onset of such complex temporal and spectral instabilities in these sources.

In this paper, generation of soliton molecules by a self-mode-locked Er/Yb double clad fiber laser is experimentally demonstrated. The optical spectrum of the bound solitons exhibits eight well defined peaks at ~1563 nm with high modulation depth. The corresponding autocorrelation measurement shows a fundamental trace with several narrow peaks, suggesting the presence of bound solitons. The obtained results demonstrate the reliability of our simple laser configuration for the formation of more robust soliton molecules as the pump power is increased. The soliton molecules exhibit repetition rate of 19.54 MHz and average power of 1.2 W, achieved with a pump power of ~4.8 W.

We report an experimental study of the supercontinuum (SC) generated by molecules of solitons (MS) and noise-like pulses (NLP) and their dependence on pump power in two different types of optical fibers: 500 m of standard fiber (SMF-28, Corning) and 100 m of high-nonlinearity fiber with a zero-dispersion slope (Furukawa HNLF-ZS). Our results show a more complex dependence of the SC spectra on pump power for the MS than for the NLP used for pump. We attribute such differences to soliton fission of MS whereas this process is already done within the NLP. We use a nonlinear optical loop mirror (NOLM) connected to the output of the fiber under test to evaluate the amplitude of ultrashort pulses, which compose SC and found that amplitude is changed strongly throughout the spectrum. The NOLM suppresses pulses with low peak power, this is especially pronounced for wavelengths longer than ∼1750 nm for both fibers, and in the region between 1450 nm–1640 nm for the high-nonlinearity fiber.

We present an experimental study of complex noise-like pulse dynamics in a passively mode-locked figure-eight fiber laser, by performing simultaneous temporal and spectral mapping of the waveform sequences. The simultaneous measurements allow us to relate temporal and spectral events. We found in particular that the evolution of energy and of temporal features such as the number and width of the wave packets is correlated to spectral variations, namely of the central wavelength and bandwidth of the instantaneous spectrum. The simultaneous temporal and spectral measurements also allowed a substantial improvement in the precision of the latter, which was performed using the dispersive Fourier transform method. In particular, this enhanced precision allowed measuring the subtle spectral differences between the two laser outputs and tracking their evolution over the cycles, providing crucial information that allowed to determine the physical phenomena involved in the observed dynamics.

We investigate a new configuration of a mode-locked fiber laser by using a nonlinear polarization rotation-based design to generate soliton pulses with low repetition rate. Unlike with previously reported configurations, we introduce a Faraday mirror after the first half of the cavity length to counteract the nonlinear polarization rotation effects. The total cavity length is 437 m including a 400-m long twisted SMF-28 fiber. The fiber was twisted to cancel the linear birefringence and to ensure that the polarization ellipticity is not altered as the pulse travels along the fiber. The strict control of polarization yields a stable relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. Depending on the polarization state we observed three different emission regimes, the single soliton regime (SR), conventional noise-like pulses (NLP) and noise-like square-waveform pulse (NLSWP). In the SR, a 467.2 kHz train of solitons was obtained with pulse duration of 2.9 ps at 1558.7 nm.

We report an experimental study of passive harmonic mode-locking in an all-fiber switchable dual-wavelength Er/Yb double-clad laser. The proposed scheme supports single- and dual-wavelength operation of mode-locked pulses with rectangular, h-like and trapezoidal shapes in a noise-like pulse regime. Single-wavelength emissions at λ₁ = 1545.1 and λ₂ = 1563.6 nm were obtained for pump power values of 9.42 and 6.31 W, achieving pulse durations of up to 18 and 11.8 ns, respectively. At an intermediary pump power of 7.5 W, dual-wavelength emission is obtained and pulses of around 3.59 ns are generated. Additionally, the transition dynamics until 4th-order harmonic mode-locking is also observed. Different laser operation regimes of fundamental and different orders of harmonic mode-locking, with rectangular, h-shaped or trapezoidal shaped pulses are obtained with the same laser configuration with simple and well-defined plates and pump power adjustments.

We report an extensive experimental study of a dual-wavelength (1530 and 1560 nm) passively mode-locked fiber laser in a ring configuration with strict control of the polarization state. Different types of laser operation are identified, which are classified into ten mode locking regimes (solitons-noise-like pulsing, solitons–solitons, solitons-CW, bound solitons-CW, solitons (1530 nm), CW-solitons, CW-bound solitons, Q-switched-like noise-like pulsing, steady noise-like pulsing at 1530 nm and intermittent mode locking), which are mapped in terms of the polarization settings (ellipticity and azimuth). The resulting map establishes, in a clear and repeatable way, the relation existing between each mode locking regime and the polarization adjustment, which allows controlling at the same time intracavity losses, the gain profile, the cavity spectral transfer function, as well as the nonlinear switching characteristic.

We demonstrate the dual-wavelength quasi mode-locked operation of a passively mode-locked Er-doped fiber ring laser with twisted fiber in the cavity and a double-pass amplifier with a Faraday mirror. The configuration allows very strict control of the polarization. We observed synchronous dual-wavelength generation of noise-like pulses (NLP) with spectra centered at 1534 nm and 1562 nm. Rotation of the azimuth of the radiation propagating in the cavity caused a switching between the generation of NLPs and packets of pulses with typical solitons spectrum. In the latter regime, we observed partially synchronous sub-pulses at two different wavelengths.

In this paper, a double-clad Er/Yb fiber laser with self-Q-switched and continuous wave operation depending on the pump power range is experimentally demonstrated. The linear cavity is formed on one side by a pair of cascaded tunable fiber Bragg gratings used for the selection and tuning of the generated laser lines. On the opposite side, a fiber optical loop mirror with high birefringence fiber in the loop is used to adjust the intra-cavity losses to obtain dual-wavelength emission by temperature changes on the fiber loop. Continuous wave dual-wavelength laser operation is obtained for tunable separation of the generated laser lines in a range from 1 to 7 nm, maximum output power of 3.6Wwith a pump power of 10Wand laser wavelengths linewidth of ~0.2 nm. Self-Q-switched laser pulses are obtained with low pump power in a range from 322 to 890 mW. Q-switched pulses with minimum pulse duration of ~1.5 _s and maximum pulse energy of ~3.5 _J are obtained.