Lingjie Kong

Tunable all-normal-dispersion Yb-doped mode-locked fiber lasers

We experimentally investigate continuous wavelength tunability in an all-normal-dispersion Yb-doped mode-locked fiber laser with an Yb-doped fiber of a fixed length. The spectral tuning over 46.3 nm, from 1024.5 to 1070.8 nm, is achieved. Spectral dynamics with different pumping levels are demonstrated. The central wavelength of the dissipative solitons shifts 8 nm towards short wavelength with pump power increasing from 168 to 456 mW.

Enhancement of cascaded four-wave mixing via optical feedback

A scheme is proposed to enhance the cascaded four-wave mixing (CFWM) generation, by introducing an optical feedback to the input port. Experimental and numerical results show that more efficient CFWM generation can be obtained by the scheme. The number of CFWM products is increased, as well as the powers of most CFWM products are improved.

Operating regime analysis of a mode-locking fiber laser using a difference equation model

We proposed a difference equation model for describing fiber lasers mode-locked with nonlinear polarization evolution. Based on this model we could characterize the intra-cavity nonlinear dynamics, such as steady single pulse emission, period multiplication, multi-pulsing and chaos. The influence of adjusting the wave-plate was studied. By shifting the linear phase bias, overdriving of the saturable absorber was relieved as in experiments, and it was found that the transition of intra-cavity dynamics depends on the modulation depth.

Contrast and resolution enhanced optical sectioning in scattering tissue using line-scanning two-photon structured illumination microscopy

Optical sectioning imaging with high spatial resolution deep inside scattering samples such as mammalian brain is of great interest in biological study. Conventional two-photon microscopy deteriorates in focus when light scattering increases. Here we develop an optical sectioning enhanced two-photon technique which incorporates structured illumination into line-scanning spatial-temporal focusing microscopy (LTSIM), and generate patterned illumination via laser intensity modulation synchronized with scanning. LTSIM brings scattering background elimination and in-focus contrast enhancement, and realizes nearly 2-fold increase in spatial resolution to ∼208 nm laterally and ∼0.94 µm axially. In addition, the intensity modulated line-scanning implementation of LTSIM enables fast and flexible generation of structured illumination, permitting adjustable spatial frequency profiles to optimize image contrast. The highly qualified optical sectioning ability of our system is demonstrated on samples including tissue phantom, C. elegans and mouse brain at depths over hundreds of microns.

Multiplexed static FBG strain sensors by dual-comb spectroscopy with a free running fiber laser

We demonstrate a novel FBG sensor system by dual-comb spectroscopy with a single fiber laser cavity, which enables interrogation of multiplexed FBG strain sensors with 0.5 με resolution in a large dynamic range of 520 με.

Operating regime analysis of mode-locking fiber laser with difference equation model

We proposed a difference equation model for fiber lasers mode-locked with nonlinear polarization evolution. It can be used to characterize intra-cavity nonlinear dynamics, such as steady one-pulse, period multiplication, multi-pulsing and chaos. The influence of adjusting wave-plate is also studied. By shifting linear phase bias, overdriving of saturable absorber is solved, and pulses of higher energy could be achieved. The modulation depth is found to affect the transition of intra-cavity dynamics.

Polarization dynamics in dissipative soliton fiber lasers mode-locked by nonlinear polarization rotation

Based on coupled Ginzburg-Landau equations and Jones matrixes, we numerically studied the polarization dynamics in dissipative soliton fiber lasers mode-locked by nonlinear polarization rotation. It is found that the components at two polarization axes are of different energies and spectra, which are intrinsic conditions of high-energy pulse generation. Besides, the non-uniform polarization rotation in dissipative soliton fiber lasers can act as a spectral filter, assisting mode-locking.