Noise-like pulsing and non-stationary operation of passively mode-locked fiber lasers: Recent advances and applications Chapter uri icon

abstract

  • Passively mode-locked fiber lasers are flexible low-cost sources that can be tailored in order to produce a wide variety of optical pulses, including conservative solitons, dispersion-managed solitons and dissipative solitons, among others. Such regimes correspond to stationary mode locking operation of these sources, in which stable trains of identical pulses at the cavity frequency are produced. Aside from these regimes, however, vast regions in the parameter space correspond to nonstationary modes of operation of these lasers, which have recently started to be explored. One particular example of a not-so-stable mode of operation of passively mode-locked fiber lasers is the noise-like pulsing regime. Noise-like pulses (NLPs) are large bunches of optical radiation with a fine inner structure that is subject to an extremely complex chaotic evolution. Due to their unique properties, such as high energy and broad bandwidth, as well as their possible connection with extreme-intensity events known as optical rogue waves, NLPs are currently attracting increasing interest for both fundamental research and applications. However, because of their extreme complexity and variability, characterizing these pulses experimentally is a challenging task. This work summarizes the recent advances of our group in the study of NLP generation in the 1550 nm region. Different fiber laser architectures are considered. Record single pulse energies of 0.3 µJ (~1000 times the energy of a conservative soliton) and spectral bandwidths of several hundred nm (~10 times the doped fiber bandwidth) are reported. Besides, using an original measurement technique, we retrieve information on the intimate inner structure of NLPs and confirm their connection with optical rogue waves. The potential of these pulses for applications is also highlighted, by demonstrating the generation of a broad supercontinuum spectrum through the propagation of NLPs in a piece of conventional telecommunications fiber, which is thus not optimized for this purpose, in particular in terms of nonlinear coefficient and dispersion. In spite of the chaotic inner dynamics of NLPs, in many cases a single bunch circulates in the cavity, producing on a scope a regular train of periodic envelopes, which mimics stationary regimes and justifies that the term “partial” mode locking is sometimes associated with the NLP regime. In some unclear circumstances, however, a NLP may split into multiple fragments, which may synchronize, yielding harmonic mode locking, or trigger the onset of a wide spectrum of puzzling collective dynamics. In this work, NLP splitting, harmonic mode locking from order 2 to more than 1200, as well as a broad range of complex NLP dynamics are described in a variety of laser configurations. Besides, connections between NLPs and optical solitons are also experimentally evidenced. Finally, a particularly puzzling dynamics, a hybrid regime in which a NLP coexists with wavelength-shifted bunches of solitons in a ring laser cavity, is also reported. © 2017 Nova Science Publishers, Inc.

publication date

  • 2017-01-01