Invited column-“Ultra-fast fiber laser technology (II)”
2019, 48(1): 103001.
doi: 10.3788/IRLA201948.0103001
Femtosecond optical frequency combs have introduced revolutionary promotions to precision optical spectroscopy and metrology, and have been hot topics of laser technologies and applications for two decades. In this article, the affects of intracavity dispersion and mode-locking mechanism on carrier-envelope phase slip frequency (fCEO) of femtosecond laser pulse trains were researched based on a femtosecond Ytterbium-doped fiber laser with 250 MHz repetition rate. By optimizing the intracavity dispersion, pumping power, and detection methods, 49 dB signal-noise-ratio fCEO beat signal was obtained which then was stabilized it to a stability of 3.210-10 in 1 second, and a stability of 3.410-13 (1 s) of frep was also achieved. In addition, the effects of pulse chirping on the output pulse duration of a fiber amplifier was researched based on a piece of large-mode-area photonic crystal Yb doped fiber. Under 60 W of pumping power from a laser diode at 976 nm wavelength, 23 W average output power from the amplifier with 66 fs pulse duration and 250 MHz repetition rate was achieved when the seed pulses were carring -3.8104 fs2 pre-chirping dispersion.
2019, 48(1): 103002.
doi: 10.3788/IRLA201948.0103002
Multi-wavelength ultrafast lasers play an important role in a variety of applications ranging from optical communications to medical diagnostics and optical sensing. Two-dimensional (2D) materials, including graphene, topological insulators, transition metal dichalcogenides, and phosphorene, have witnessed a very fast development of both fundamental and practical aspects in ultrafast photonics since 2009. Their unique nonlinear optical properties enable them to be used as excellent saturable absorbers with fast responses and broadband operation and can be easily integrated into lasers. Here, we review the recent advances in the exploitation of these 2D materials in multi-wavelength ultrafast lasers. Interestingly, study found that, 2D materials-based nonlinear optical device is an ideal platform for nonlinear pulse dynamics study. Thus, versatile pulse patterns, including dissipative soliton, rectangular pulse, and bright-dark soliton pair, are also demonstrated. Finally, current challenges and future application opportunities of 2D materials-based multi-wavelength ultrafast lasers are presented.
2019, 48(1): 103003.
doi: 10.3788/IRLA201948.0103003
All-optical modulator plays an important role for various all-optical applications in optical communication. An all-optical modulator was mainly investigated based on few-layer molybdenum disulfide (MoS2)-polyvinyl alcohol (PVA) thin films. In addition, an all-optical modulator based on few-layer tungsten disulfide (WSe2)-polyvinyl alcohol (PVA) thin film was also demonstrated. The modulator was based on polarization interference and the thermo-optic effect of TMDs-PVA thin film. A long-time stable modulated output was obtained. By absorbing the pump at 980 nm, MoS2 or WSe2 generates heat, changes the refractive index of thin film and modifies the polarization of the incident light at 1 550 nm. The obtained thermal all-optical modulator based on MoS2-PVA thin film has a rise time of 526 s.
2019, 48(1): 103004.
doi: 10.3788/IRLA201948.0103004
The soliton-effect compression of femtosecond optical pulses in highly nonlinear silica-core photonic crystal fiber at near-infrared spectrum region (especially at 850 nm) was numerically investigated by full-vector finite element method and split-step Fourier method. A novel SiO2 core photonic crystal fiber with an anomalous group velocity dispersion (2=-50.698 ps2/km), small higher-order dispersions and high nonlinearity (=268.419 1 W-1/km) for efficient soliton-effect compression of femtosecond optical pulses was proposed, the nonlinear Schrodinger equation including higher-order dispersions and Raman scattering was derived. The effect of the Gaussian pulses compression in HN-PCF was numerically investigated by taking account of the fiber length and the soliton order, and the second to fifth orders dispersion were analyzed. The research results show that Q factor and compression factor are maximum at the soliton order of 8. The effect of compression is best when the input pulse's energy P0=3 357.8 W. By optimizing the geometric and optical parameters of the fiber, the high-quality ultrashort optical pulses with little pedestal energy are obtained.
2019, 48(1): 103005.
doi: 10.3788/IRLA201948.0103005
The effects of periodic spectral modulation on self-similar amplification systems of femtosecond pulses were studied by numerical simulation. Femtosecond pulses with spectral modulation amplified in self-similar amplification theoretical model were simulated, by which the impacts of variables of seed pulses, such as arbitrary phase shift, modulation depth and period, on output results were analyzed. According to the simulation, arbitrary phase shift changes modulated spectral shape, but temporal results of self-similar amplification will not be affected. Besides, large modulation periods make sub-pulses inseparable from main-pulses, disturbing the self-similar amplification process, while small modulation periods bring a longer delay for sub-pulses, making the amplification of main-and sub-pulse independently. This conclusion is still tenable when modulation depth changes.
