This work is devoted to the study of the generation regime of an ultrashort pulse bunch in an erbium-doped fiber laser with hybrid mode-locking in the region of a low positive total intra-cavity group velocity dispersion. The pulse bunch has an optical spectrum 33 nm wide with a central wavelength of 1530 nm and has 2 pulses inside with a duration of ~143 fs at the full-width-half-maximum. The radio frequency spectrum in the region of the main pulse repetition rate, equal to ~8.5 MHz, demonstrates, depending on the pump power, the presence of 4 to 8 side peaks associated with the second pulse in the bunch. A comparison of the single-pulse and multi-pulse regimes demonstrates a twofold increase in the average output optical power of a pulse bunch for equal pump power and cavity parameters.
In this paper, we have studied ML features in a sub-200-fs erbium-doped all-fiber laser based on a saturable absorber obtained by high-pressure-high-temperature treatment of commercially available single-walled carbon nanotubes. We have shown that there is a significant effect on the ultrafast optical properties of saturable absorber due to the high-density well-aligned structure of newly-developed single-walled carbon nanotubes and related it to the mode-locked laser performance. We have obtained a low-intensity-noise ultra-short stretched pulse generation with a repetition rate of 42.22 MHz, a spectral pulse width of 30 nm, and average output power of 11.3 mW with long-term stability of ~ 0.06% during 3 h measurement time
In this paper, we have developed a chirped-pulse Er-doped all-fiber ultrashort pulse (USP) laser suitable for highresolution Raman distributed temperature sensor (RDTS) system application. Chirped-pulse regime which is determined by the positive net-cavity dispersion of +0.12 ps2 allows us to increase the energy of the pulses for effective signal-to-noise ratio in receiving system. It also helps to avoid the influence most of nonlinear effects due to relatively long pulses duration of ~24.6 ps. The average power of the pulses is estimated to be ~1 mW from master oscillator, and currently increased up to ~15 mW by power amplifier. A relatively low repetition rate of ~ 7.925 MHz with signal-to-noise ratio ~ 69 dB was achieved using the resonator length of ~25.6 m. To characterize short-term stability of the obtained regime we have also measured the relative intensity noise of the laser, which is < -107 dBc/Hz in the range of 3 Hz - 1 000 kHz.
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.
Nowadays fiber optic Raman distributed temperature sensors (RDTS) are broadly used for e.g. fire detection, gas leaks detection in pipelines and aircraft icing monitoring. The most common sources of probe pulses for RDTS are CW lasers with external intensity modulation or Q-switched lasers with a pulse duration of several tens of nanoseconds which limits the RDTS effective spatial resolution to a few meters. In this paper we have developed an Er-doped ultrashort pulse (USP) mode-locked fiber laser and implemented it to Raman distributed temperature sensor.This feature allow us to achieve high spatial resolution (down to several centimeters) and high signal-to-noise ratio in the receiving system. An all-fiber erbium-doped laser of 180 fs pulse duration and an average output power of 30 mW was used as a source of probing pulses. We have studied limiting factors of fiber sensor effective length such as high pulse repetition rate of 12.2 MHz and intensity noise of the USP laser (relative intensity noise RIN ~ 6.3 ∙ 10-4). Furthermore, the peak power of the USP laser has to be at kW level to get high signal-to-noise ratio in the receiving system and pulse duration < 100 ps at full-width-half-maximum for desirable spatial resolution of ~2 cm. Moreover, we have developed an experimental prototype of RDTS with the spatial resolution of ~ 0.1 m limited by the receiving system according to the detector bandwidth of 2 GHz, the effective sensor length of 3 m and ±1.5 °C temperature measurement error. As a result, a list of requirements for a new laser source for distributed temperature sensor was formulated.
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.
Recently similariton (or self-similar pulse) fiber lasers have attracted great attention due to their capabilities of highenergy
pulse generation that could find different applications in science and industry. Moreover it is very important to
reach stable pulse generation for the application as a frequency divider in optical frequency standard. Hybrid modelocking
mechanism was used for obtaining stable similariton generation at 38 MHz pulse repetition frequency. It
involves two types of mode-locking mechanisms in the cavity - saturation of carbon nanostructures absorber (recovery
time Trt ~ 500 fs) and nonlinear polarization evolution based on the nonlinear Kerr-effect (Trt ~ 10 fs). It was shown that
total intracavity dispersion should be slightly positive for generating stable similaritons with duration of less than 90 fs
and spectral bandwidth of more than 50 nm at 11.2 mW output average power that could be further applied in an all-fiber
MOPA setup.
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