Maria Chernysheva

Nonlinear Amplifying Loop-Mirror-Based Mode-Locked Thulium-Doped Fiber Laser

We present an SESAM mode-locked thulium-doped fiber laser incorporating nonlinear amplifying loop mirror with intracavity and external group velocity dispersion control, which generates sub-300-fs near-transform-limited pulses at 1920-nm wavelength, with 106-mW maximum average output power. The dispersion control was realized by implementing a low-loss highly doped germanium silica fiber.

High Power Q-Switched Thulium Doped Fibre Laser using Carbon Nanotube Polymer Composite Saturable Absorber.

We have proposed and demonstrated a Q-switched Thulium doped fibre laser (TDFL) with a ‘Yin-Yang’ all-fibre cavity scheme based on a combination of nonlinear optical loop mirror (NOLM) and nonlinear amplified loop mirror (NALM). Unidirectional lasing operation has been achieved without any intracavity isolator. By using a carbon nanotube polymer composite based saturable absorber (SA), we demonstrated the laser output power of ~197 mW and pulse energy of 1.7 μJ. To the best of our knowledge, this is the highest output power from a nanotube polymer composite SA based Q-switched Thulium doped fibre laser.

Carbon nanotubes for ultrafast fibre lasers

Abstract Carbon nanotubes (CNTs) possess both remarkable optical properties and high potential for integration in various photonic devices. We overview, here, recent progress in CNT applications in fibre optics putting particular emphasis on fibre lasers. We discuss fabrication and characterisation of different CNTs, development of CNT-based saturable absorbers (CNT-SA), their integration and operation in fibre laser cavities putting emphasis on state-of-the-art fibre lasers, mode locked using CNT-SA. We discuss new design concepts of high-performance ultrafast operation fibre lasers covering ytterbium (Yb), bismuth (Bi), erbium (Er), thulium (Tm) and holmium (Ho)-doped fibre lasers.

Higher-Order Soliton Generation in Hybrid Mode-Locked Thulium-Doped Fiber Ring Laser

A thulium-doped all-fiber laser passively mode-locked by the co-action of nonlinear polarization evolution and single-walled carbon nanotubes operating at 1860-1980 nm wavelength band is demonstrated. Pumped with the single-mode laser diode at 1.55 μm laser generates near 500-fs soliton pulses at repetition rate ranging from 6.3 to 72.5 MHz in single-pulse operation regime. Having 3-m long cavity average output power reached 300 mW, giving the peak power of 4.88 kW and the pulse energy of 2.93 nJ with slope efficiency higher than 30%. At a 21.6-m long ring cavity average output power of 117 mW is obtained, corresponding to the pulse energy up to 10.87 nJ and a pulse peak power of 21.7 kW, leading to the higher-order soliton generation.

Transform-limited pulse generation in normal cavity dispersion erbium doped single-walled carbon nanotubes mode-locked fiber ring laser

We demonstrate an erbium doped fiber ring laser mode-locked with a carboxymetylcellulose high-optical quality film with dispersed single-walled carbon nanotubes (SWCNT). The laser with large normal net cavity dispersion generates near bandwidth-limited picosecond inverse modified soliton pulses at 1.56 µm.

Double-wall carbon nanotube hybrid mode-locker in Tm-doped fibre laser: a novel mechanism for robust bound-state solitons generation

The complex nonlinear dynamics of mode-locked fibre lasers, including a broad variety of dissipative structures and self-organization effects, have drawn significant research interest. Around the 2 μm band, conventional saturable absorbers (SAs) possess small modulation depth and slow relaxation time and, therefore, are incapable of ensuring complex inter-pulse dynamics and bound-state soliton generation. We present observation of multi-soliton complex generation in mode-locked thulium (Tm)-doped fibre laser, using double-wall carbon nanotubes (DWNT-SA) and nonlinear polarisation evolution (NPE). The rigid structure of DWNTs ensures high modulation depth (64%), fast relaxation (1.25 ps) and high thermal damage threshold. This enables formation of 560-fs soliton pulses; two-soliton bound-state with 560 fs pulse duration and 1.37 ps separation; and singlet+doublet soliton structures with 1.8 ps duration and 6 ps separation. Numerical simulations based on the vectorial nonlinear Schr¨odinger equation demonstrate a transition from single-pulse to two-soliton bound-states generation. The results imply that DWNTs are an excellent SA for the formation of steady single- and multi-soliton structures around 2 μm region, which could not be supported by single-wall carbon nanotubes (SWNTs). The combination of the potential bandwidth resource around 2 μm with the soliton molecule concept for encoding two bits of data per clock period opens exciting opportunities for data-carrying capacity enhancement.

Isolator-free switchable uni- and bidirectional hybrid mode-locked erbium-doped fiber laser

An Erbium-doped fibre ring laser hybrid mode-locked with single-wall carbon nanotubes (SWNT) and nonlinear polarisation evolution (NPE) without an optical isolator has been investigated for various cavity conditions. Precise control of the state of polarisation (SOP) in the cavity ensures different losses for counter-propagating optical fields. As the result, the laser operates in quasi-unidirectional regime in both clockwise (CW) and counter-clockwise (CCW) directions with the emission strengths difference of the directions of 22 dB. Furthermore, by adjusting the net birefringence in the cavity, the laser can operate in a bidirectional generation. In this case, a laser pumped with 75 mW power at 980 nm generates almost identical 790 and 570 fs soliton pulses with an average power of 1.17 and 1.11 mW. The operation stability and pulse quality of the soliton pulses in both unidirectional regimes are highly competitive with those generated in conventional ring fibre lasers with isolator in the cavity. Demonstrated bidirectional laser operation can find vital applications in gyroscopes or precision rotation sensing technologies.

Pulse bursts generation at 10 GHz intra-burst repetition rate in Quasi-lossless mode-locked erbium-doped fibre laser

‘Burst’ operating mode of mode-locked fiber lasers, presented for the first time in [1], has recently gained high potential in hard and soft tissue ablation [2, 3]. Pulse bursts consist of temporally closely spaced pulses, which during the ablation prevent rapid cycles of material heating and cooling. Bursts are typically generated at low repetition rate, which allows lower average power at the same level of the energy, therefore, avoiding long-term heat accumulation in the material. Hence, burst mode operation is superior in terms of energy required, ablation speed and avoidance of thermal effects, compared to uniform pulse trains. Currently to achieve the pulse burst generation, several acousto-optic modulators are introduced in the laser system to crop window of seed laser output pulse train or direct pulse burst generation from highly-pumped lasers [4, 5]. Here we propose a new concept of generating such pulse bursts using an ultralong mode-locked fibre laser, based on quasi-lossless concept, where the short laser cavity is enhanced with a long fiber span, forming a distributed Raman amplifier. This relaxes the restriction on non-compensated losses inherent in traditional ultralong soliton lasers and enables effective wave breaking and multiple-pulsing phenomena.

Real-time characterisation of the gyroscopic shift in a bidirectional hybrid mode-locked erbium-doped fibre laser

The prior art of the ultrafast laser gyroscopes goes back to 1981 when R.L. Fork et. al demonstrated colliding-pulse mode-locking [1] and the further discovery of the temporal overlapping of these pulses in 1990 [2]. Direct rotation measurements using laser gyroscopes are known to be more precise compared to the passive fibre optic devices, where the relative phase shift between the beams is retrieved from their interference after propagating in external passive fibre interferometer [3]. The principal limitation of the laser gyroscope sensitivity is the frequency lock-in effect, caused by residual backscattering in the cavity [4]. Ultrafast laser gyroscopes circumvent this effect since the counter-propagating ultrashort pulses interact only in two positions in the cavity and backscattering is reduced by the ultrashort width of the pulse. Here, we present an all-fibre implementation of the ultrafast laser gyroscope, and further propose measuring the gyroscopic shift in the time domain, which results in an order of magnitude improvement in the sensitivity over conventional mode-locked laser gyroscope.

Dark soliton generation from semiconductor optical amplifier gain medium in ring fiber configuration

We have investigated the mode-lock operation from a semiconductor optical amplifier (SOA) gain chip in the ring fibre configuration. At lower pump currents, the laser generates dark soliton pulses both at the fundamental repetition rate of 39 MHz and supports up to the 6th harmonic order corresponding to 234-MHz repetition rate with an output power of ~2.1 mW. At higher pump currents, the laser can be switched between the bright, dark and concurrent bright and dark soliton generation regimes.