Rapid progress in passively mode-locked fibre lasers 1-6 is currently driven by the recent discovery of new mode-locking mechanisms, namely, the self-similarly evolving pulse (similariton) 7 and the all-normal-dispersion (dissipative soliton) regimes 8,9 . These are fundamentally different from the previously known soliton 10 and dispersion-managed soliton (stretched-pulse) 11 regimes. Here, we report a fibre laser in which the mode-locked pulse evolves as a similariton in the gain segment and transforms into a regular soliton in the rest of the cavity. To our knowledge, this is the first observation of similaritons in the presence of gain, that is, amplifier similaritons, within a laser cavity. The existence of solutions in a dissipative nonlinear cavity comprising a periodic combination of two distinct nonlinear waves is novel and likely to be applicable to various other nonlinear systems. For very large filter bandwidths, our laser approaches the working regime of dispersionmanaged soliton lasers; for very small anomalous-dispersion segment lengths it approaches dissipative soliton lasers.Passively mode-locked fibre lasers are being used in a diverse range of applications, including optical frequency metrology 12,13 , material processing 14 and terahertz generation 15 . Historically, major advances in laser performance have followed the discovery of new mode-locking regimes [1][2][3][4][5][6]16 , so there is always a strong motivation to search for new regimes.The physics of mode-locked fibre lasers comprises a complex interaction of gain, dispersion and nonlinear effects 17 . Such lasers are a convenient experimental platform for the study of nonlinear waves subject to periodic boundary conditions and dissipative effects. These characteristics profoundly alter the behaviour of nonlinear waves, so this area of research is interesting in its own right. In addition to the vast literature on optical solitons . These similaritons existed in segments of the cavity without any gain and loss to avoid the large spectral broadening that is characteristic of amplifier similaritons. Formation of a self-consistent solution in a laser cavity requires the compensation of spectral broadening, which has proved to be non-trivial 5 . Despite numerical predictions of their existence dating back almost a decade 26 , amplifier similaritons had yet to be observed in a laser cavity.Here, we present our experimental and theoretical work demonstrating an entirely new mode-locking regime, in which the pulse propagates self-similarly in the gain fibre with normal dispersion, and following spectral filtering, gradually evolves into a soliton in the rest of the cavity, where the dispersion is anomalous. All mode-locked lasers to date have had a single type of nonlinear wave propagating within the cavity; however, in our laser, distinctly different similariton and soliton pulses co-exist, demonstrating that transitions between these are possible. Remarkably, this construct is extremely robust against perturbations. Although the pulse expe...

Intensity noise of mode-locked fiber lasers is characterized systematically for all major mode-locking regimes over a wide range of parameters. We find that equally low-noise performance can be obtained in all regimes. Losses in the cavity influence noise strongly without a clear trace in the pulse characteristics. Given that high-energy fiber laser oscillators reported to date have utilized large output coupling ratios, they are likely to have had high noise. Instabilities that occur at high pulse energies are characterized. Noise level is virtually independent of pulse energy below a threshold for the onset of nonlinearly induced instabilities. Continuous-wave peak formation and multiple pulsing influence noise performance moderately. At high energies, a noise outburst is encountered, resulting in up to 2 orders of magnitude increase in noise. These results effectively constitute guidelines for minimization of the laser noise in mode-locked fiber lasers.

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Abstract:We report order-of-magnitude spectral breathing in a dispersion-managed Er-fiber laser with an intracavity bandpass filter. This is to our knowledge the highest of any laser reported. Pulse energy is 1.7 nJ, width is 110 fs.OCIS code: (060.7140) Ultrafast processes in fibers; (140.3510) Lasers, fiber.Ultrafast fiber lasers attract much interest due to their potential to replace solid-state lasers in applications such as materials processing and optical frequency metrology owing to their excellent stability, simplicity of operation and low cost. Pulse formation is dominated by a rich interplay between group velocity dispersion (GVD) and nonlinear effects [1,2]. Developments leading to better performance are typically triggered by new pulse shaping concepts and better understanding of the underlying dynamics.Here, we report an Er-fiber laser with a dispersion-managed cavity containing a narrow-band optical filter. The mode-locked operation is very robust and remarkably, the spectral width of the pulse changes by as much as 7 times within one roundtrip. This is the highest spectral variation reported to our knowledge for any laser cavity. Spectral broadening is inherently a nonlinear process. In this sense, this laser could be viewed as the most "nonlinear laser". The surprising feature here is that this is observed stably within a laser cavity, subject to periodic boundary conditions, i.e., all changes must be undone at the end of each roundtrip.The experimental arrangement is illustrated in Fig. 1. The fiber section consists of 3 m of regular single-mode fiber (SMF) and 1 m of highly doped Er-doped fiber, followed by another 0.55 m of SMF. The Er-doped fiber has mode field diameter (MFD) of 3.57µm, numerical aperture (NA) of 0.322 and GVD of 76.8 fs 2 /mm at 1.55 µm, while the SMF had MFD of 10.4 µm, NA of 0.14, and GVD of -22.83 fs 2 /mm. The net GVD of the laser cavity was calculated to be about 0.011 ps 2 . A maximum of 350 mW of pump light at 980 nm from a laser diode is delivered to the cavity via a 980/1550 nm wavelength division multiplexer. An optical isolator ensures unidirectional operation, which facilitates self-starting operation. Mode-locking is initiated and stabilized with nonlinear polarization evolution (NPE). Threshold pump power for modelocking is 300 mW. Self-starting modelocked operation is achieved readily and very stably by adjustment of the waveplates. The mode-locked laser produces a stable pulse train with 42.7 MHz of repetition rate. Although cw output power can be as high as 150 mW, in modelocked operation the average power is limited to 116 mW, which corresponds to an intracavity pulse energy of 2.7 nJ. The results of the characterization of the laser are shown in Fig. 2. We measured 12 nm, 64 nm, and 85 nm of full-width at half-maximum (FWHM) values for the optical spectra from 1% port, 5% port, and NPE port, respectively ( Fig. 2 (a-b)). The corresponding spectral breathing ratio is 7.1. The laser generates ~700-fs-long chirped pulses, which are compressed to 110 fs with a...

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Repetition-frequency stabilization of a Yb-doped fiber laser to the Cesium standard is reported. Laser amplitude and phase noise is characterized. Performance is limited to 2x10 -14 at 100000 averaging time by intrinsic stability of the Cs-standard. ©2010 Optical Society of America Femtosecond laser frequency comb has revolutionized frequency metrology in recent years. While most of the initial activity utilized Ti:sapphire lasers, frequency combs generated from fiber lasers are increasingly important due to their advantages in long-term stability, cost-efficiency and operation-convenience [1]. Extremely long durations of uninterrupted operation are being reported from mode-locked fiber lasers. However, most of the activity is centered on Er-doped fiber lasers, with very few reports [2] utilizing Yb-doped fiber lasers, even though this gain medium offers superior technical performance in nearly every aspect. In particular, all-normal-dispersion (ANDi) lasers have been attracting much attention with their simplified cavity, increased ease-of-mode-locking and good technical performance [3]. However, to date, there is no study exploring the long-term stability of an ANDi laser, nor its use for comb generation. Here, we demonstrate for the first time to our knowledge, long-term (over several days) stabilization of an ANDi Yb-doped fiber laser to a Cs frequency standard. Characterization of short-term amplitude and phase noise characterization of the oscillator coupled with its long-term stability demonstrates its potential for use as a frequency-comb generator.The Yb-doped fiber laser has been constructed with a focus on its long-term stability and ease of transportation ( Fig. 1(a)). The laser includes both a fast, piezo-based fiber stretcher and a slow, motorized translation stage to control the cavity length. The motorized stage is used to roughly set the repetition rate to the desired value and the fast stretcher is used for electronic locking to the reference. The repetition rate is 108.33 MHz (12 nd sub-harmonic of 1.3 GHz), and the laser produces 0.8 nJ-energy chirped pulses, which can be dechirped to 127 fs. The optical spectrum is characteristic of this laser type (inset of Fig.

Fiber lasers are attractive with their simplicity, high powers and low cost. However, propagation of short pulses in optical fiber leads to nonlinear effects, which limit the technical performance. These effects drive rich dynamics, which is interesting from a fundamental perspective. The nonlinear waves community has unraveled the fascinating world of solitons and similaritons through experiments in fibers. This paper overviews the recent development of the soliton-similariton laser. The original similariton laser was the first to work with nonlinear effects, rather than minimizing or compensating them. In the soliton-similariton laser, the propagation is strongly nonlinear everywhere. © 2011 IEEE