In this work, we study a 215-m-long figure-of-eight fiber laser including a double-clad erbium-ytterbium fiber and a nonlinear optical loop mirror based on nonlinear polarization evolution. For proper adjustments, self-starting passive mode-locking is obtained. Measurements show that the mode-locked pulses actually are noise-like pulses, by analyzing the autocorrelation, scope traces and the very broad and flat spectrum extending over a record bandwidth of more than 200 nm, beyond the 1750 nm upper wavelength limit of the optical spectrum analyzer. Noise-like pulsing was observed for moderate and high pump power preserving the same behavior, reaching pulse energies as high as 300 nJ, with pulse durations of a few tens of ns and a coherence length in the order of 1 ps. Stable fundamental mode locking as well as harmonic mode locking up to the 6th order were observed. The bandwidth was further extended to more than 450 nm when a 100-m piece of highly nonlinear fiber was inserted at the laser output. The enhanced performances obtained compared to other similar schemes could be related to the absence of a polarizer in the present setup, so that the state of polarization along the cavity is no longer restricted.

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.

Some complex dissipative dynamics associated with the noise-like pulse (NLP) regime of a passively mode-locked erbium-doped fiber laser are studied numerically. By means of a convenient 3D mapping of the spatio-temporal pulse evolution, for properly chosen dispersion parameters, several puzzling dissipative dynamics of NLPs are identified, including the expelling of sub-packets that move away from the main bunch, the sudden extinction of isolated sub-pulses, the collision between different internal fragments travelling at different speeds, the rising of sub-pulses, the formation of complex trajectories by substructures that first move away and then return to the main bunch, and so on. In addition, the emergence of optical rogue waves (ORWs) within NLPs is also demonstrated numerically; to help understand these behaviors evidenced in the time domain, spectral analyzes were also performed that show, among other things, that the spectrum of a NLP is notoriously distorted when it hosts an ORW phenomenon. These numerical results are consistent with previously published experimental results.

We propose an all-fiber-optic multimode interferometer for measuring liquid refractive index. The interferometer was manufactured by using arc splice technique between standard single mode fiber and optical microfiber. A maximum refractive index sensitivity of 112dB/RIU is experimentally demonstrated. In addition, thermal effects exhibit low phase modulation (12pm/°C) with minimal intensity variations (-10.7*10-3dB/°C), as a result, cross-sensitivity around 0.05*10-6 RIU/ °C and 0.9 *10-6 RIU/ °C are obtained for intensity and phase modulation. The stability analysis shows minimal wavelength and power variations, 0.01nm and 0.27dB respectively, for constant temperature and refractive index. Spatial frequency analysis was explored as an alternative method to measure liquid refractive index avoiding thermal effects.

We study numerically supercontinuum generation (SCG) in four different 10-cm-long photonic crystal fibers (PCFs) at 800 nm and ~1060 nm, whose parameters are found in the literature, comparing the performance of noise-like pulses (NLPs) and ultrashort pulses (USPs) as the pump. Averaging hundreds of spectra produced by NLPs from two passively mode-locked fiber lasers (thulium and ytterbium), smooth and uniform curves similar to experimental ones were achieved, requiring low or moderate input peak powers. In contrast, spectra exhibiting poor flatness with strong fluctuations up to 24 dB were obtained when using USPs as the pump.

A tunable multi-wavelength fiber laser is proposed and demonstrated based on two main elements: an erbium-doped fiber ring cavity and compact intermodal fiber structure. The modal fiber interferometer is fabricated using the cost-effective arc splice technique between conventional single-mode fiber and microfiber. This optical fiber structure acts as a wavelength filter, operated in reflection mode. When the refractive index and temperature variations are applied over the fiber filter, the ring laser cavity provides several quad-wavelength laser spectra. The multi-wavelength spectra are tuned into the C-band with a resolution of 0.05 nm. In addition, the spectra are symmetric with minimal power difference between the lasing modes involved, and the average of the side mode suppression ratio is close to 37 dB. This laser offers low-cost implementation, low wavelength drift, and high power stability, as well as an effect of easy controllability regarding tuned multi-wavelength.