In this work, we propose a novel approach for stabilizing frequency comb for stable microwave generation. This approach does not require stabilization of the offset frequency, but instead employs processing the heterodyne beats from an electro-optic comb and two continuous-wave lasers that are locked to an ultrastable compact cavity. We used a free-running laser and electro-optical modulators to generate a 10 GHz frequency comb spanning over 1.3 THz, matching the frequency separation of the CW lasers. Servo control of the 10 GHz modulation frequency reduces the 10 GHz phase noise to -140 dBc/Hz phase noise at 10 kHz offset frequency. At the same time, the 10 GHz signals show frequency instability at the 10^(-13) level at integration time below 1~s. In ongoing work, we seek to implement the system using integrated laser sources, chip-scale frequency combs and millimeter-scale optical cavities.
Nowadays, real-time measurements of complex dynamics of ultrashort structures in dissipative nonlinear systems have attracted a lot of interest. In this work, we present experimentally obtained real-time dynamics of two closely-separated solitons in a mode-locked erbium fibre laser. Both solitons experienced strong temporal vibrations due to mutual attractive and repulsive forces, alongside with oscillation in their energies. We experimentally demonstrate the influence of the dispersive waves (DWs) on the dynamics of the soliton complex. Eventually, the pulses experienced a collision dynamics that resulted in the formation of a single soliton at a shifted central wavelength with highly energetic Kelly sidebands and increased background radiation. Our experimentally obtained results prove the theoretical works on soliton interaction and enrich the knowledge on the complexities of ultrashort coherent features and their behaviour in nonlinear systems.
The experimental investigation of formation of coherent structures from noise is essential for fundamental understanding of nonlinear systems. Here, we present switch-on dynamics in bidirectional mode-locked laser in spatio-temporal and frequency domains by using Dispersive Fourier Transform for both clockwise and counterclockwise directions. We have calculated cross-correlation of counter-propagating beams that reveals the dissimilarities between formation of the spectra of counter-propagating pulses. From cross-correlation we revealed periodic patterns which manifest complex exchange dynamics between the counter-propagating pulses at different stages of their mutual formation. These results will help to understand complex soliton dynamics and nonlinear systems in general.
We have studied generation of stable and low-noise de-chirped ultrashort solitons in bound states and we have experimentally demonstrated the formation multi-bound solitons with the controllable number of bound states 7 < N < 17 by pump power variation. A numerical simulation of the influence of various types of fluctuations on the generation mode was also carried out.
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.
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.
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