Lev Denisov

Generation of ultrashort pulses with minimum duration of 90 fs in a hybrid mode-locked erbium-doped all-fibre ring laser

Regimes of ultrashort pulse generation in an erbium-doped all-fibre ring laser with hybrid mode locking based on single-wall carbon – boron nitride nanotubes and the nonlinear Kerr effect in fibre waveguides are studied. Stable dechirped ultrashort pulses are obtained with a duration of , a repetition rate of , and an average output power of , which corresponds to a pulse energy of and a peak laser power of .

All-fiber mode-locked erbium-doped ring laser based on a highly-nonlinear resonator with a low-noise ultrashort pulse generation

Ultrashort pulse (USP) fiber lasers have found applications in such various fields as frequency metrology and spectroscopy, telecommunication systems, etc. For the last decade, mode-locking (ML) fiber lasers have been under carefully investigations for scientific, medical and industrial applications. Also, USP fiber sources can be treated as an ideal platform to expand future applications due to the complex ML nonlinear dynamics with a presence of high value of group velocity dispersion (GVD) and the third order dispersion in the resonator. For more reliable and robust launching of passive mode-locking based on a nonlinear polarization evolution, we used a highly nonlinear germanosilicate fiber (with germanium oxides concentration in the core ~ 50 mol. %) inside the cavity and we have obtained ultrashort stretched pulses with a high peak power and energy. In this work relative intensity noise and frequency repetition stability is improved by applying isolator-polarizer (ISO-PM) with increased extinction ratio Pext and by compensation of intracavity group-velocity dispersion from the value β2 ~ - 0.021 ps2 to ~ - 0.0053 ps2 at 1550 nm. As a result, we have obtained the low-noise stretched pulse generation with duration ~ 180 fs at a repetition rate ~ 11.3 MHz (with signal-tonoise ratio at fundamental frequency ~ 59 dB) with Allan deviation of a pulse repetition frequency for 1 s interval ~ 5,7 * 10-9 and a relative intensity noise < -101 dBc / Hz.

Ultrafast all-fiber erbium-doped ring laser mode-locked by high-density well-aligned single-walled carbon nanotubes

Ultrashort pulse (USP) fiber lasers are of great interest for their wide applications in telecommunication, frequency metrology field, dual comb spectroscopy, THz pulse spectroscopy and etc [1]. Hybrid mode-locking (ML) for USP generation have attracted a great attention due to their capabilities of enhancing pulse quality and providing reliable ML startup by taking advantage of a co-action of two saturable absorbers (SA) — a slow SA such as SESAM, single wall carbon nanotubes (SWCNTs-SA) or graphene, and a fast absorber based on nonlinear polarization evolution (NPE) effect [2]. It should be noted that compared to quantum well-based SESAMs, SWCNT-SAs benefit from much more easier and cost-effective fabrication techniques, possibility of being used in both linear and ring cavities, ultrafast carrier relaxation time and significantly enhanced noise characteristics. However, despite well-elaborated SWCNT-based film fabrication technologies, it is difficult to control such a crucial characteristic for laser mode-locking as an absorber response time during SWCNT-SA fabrication process. Moreover, a polarization dependence of saturable absorption can not be controlled since SWCNTs orientations are randomly distributed. All these features make SWCNT-SA characteristics as well as corresponding mode-locked laser performance absolutely unpredictable [3]. Recently it have been shown by X. Xu that well-aligned SWCNT-SA could be one of the ways to solve these drawbacks in ML of fiber lasers [4]. However, the proposed synthesis method is quite complicated for serial production of well-aligned SWCNT-SAs with the required parameters.

Mode-locking peculiarities in an all-fiber erbium-doped ring ultrashort pulse laser with a highly-nonlinear resonator

Today ultrashort pulse (USP) fiber lasers are in great demand in a frequency metrology field, THz pulse spectroscopy, optical communication, quantum optics application, etc. Therefore mode-locked (ML) fiber lasers have been extensively investigated over the last decade due the number of scientific, medical and industrial applications. It should be noted, that USP fiber lasers can be treated as an ideal platform to expand future applications due to the complex ML nonlinear dynamics in a laser resonator. Up to now a series of novel ML regimes have been investigated e.g. self-similar pulses, noise-like pulses, multi-bound solitons and soliton rain generation. Recently, we have used a highly nonlinear germanosilicate fiber (with germanium oxides concentration in the core ~ 50 mol. %) inside the resonator for more reliable and robust launching of passive mode-locking based on the nonlinear polarization evolution effect in fibers. In this work we have measured promising and stable ML regimes such as stretched pulses, soliton rain and multi-bound solitons formed in a highly-nonlinear ring laser and obtained by intracavity group velocity dispersion (GVD) variation in slightly negative region. As a result, we have obtained the low noise ultrashort pulse generation with duration < 250 fs (more than 20 bound pulses when obtained multi-bound soliton generation with intertemporal width ~ 5 ps) at a repetition rate ~ 11.3 MHz (with signal-to-noise ratio at fundamental frequency > 59 dB) and relative intensity noise <-101 dBc / Hz.

Enhanced high-harmonic generation in photonics crystal: theoretical and experimental studies

The effect of strong localization of electromagnetic field in colloidal photonic crystals (PCs) is considered in present paper. It is shown theoretically that due to lateral modulation of dielectric permittivity of PC the sharp peaks of light’s intensity arise at the band-gap pumping, and light field decays parametrically with depth. The light itself localises at the near-surface volume of the PC and enhances nonlinear light conversion. Theoretical model to explain generic physical picture is presented for two-dimensional PC, and the analytical results are compared with numerical simulations by finite-difference time-domain method for solving the Maxwell’s equations. The fingerprints of enhanced high harmonic generation, which are observed in our experimental studies with globular quartz PCs, justify the main theoretical predictions.

Comb Peculiarities of Dispersion-Managed Solitons in a Hybrid Mode-Locked All-Fiber Ring Laser

We studied the optical comb peculiarities of the ultra-short dispersion-managed soliton generation in an erbium-doped all-fiber ring laser hybrid mode-locked with carbon:boron nitride single-walled nanotubes in the co-action with a nonlinear polarization evolution. A stable low-intensity-noise optical comb was obtained with a narrow single comb linewidth of 18.1 kHz based on dechirped 90-fs pulses with a repetition rate of 42.22 MHz, a spectral pulse width of 56 nm, and an average output power of 16.7 mW corresponding to 4.4-kW maximum peak power and 0.4-nJ pulse energy.