Passive mode-locked Er-doped fiber laser pulse generation based on titanium disulfide saturable absorber

In this study,titanium disulfide(TiS_(2))polyvinyl alcohol(PVA)film-type saturable absorber(SA)is synthesized with a modulation depth of 5.08%and a saturable intensity of 10.62 MW/cm^(2) by liquid-phase exfoliation and spin-coating methods.Since TiS2-based SA has a strong nonlinear saturable absorption property,two types of optical soliton were observed in a mode-locked Er-doped fiber laser.When the pump power was raised to 67.3 mW,a conventional mode-locked pulse train with a repetition rate of 1.716 MHz and a pulse width of 6.57 ps was generated,and the output spectrum centered at 1556.98 nm and 0.466 nm spectral width with obvious Kelly sidebands was obtained.Another type of mode-locked pulse train with the maximum output power of 3.92 mW and pulse energy of 2.28 nJ at the pump power of 517.2 mW was achieved when the polarization controllers were adjusted.Since TiS2-based SA has excellent nonlinear saturable absorption characteristics,broad applications in ultrafast photonic are expected.

Structured vortices generated by metasurface holography

Highly customized and miniaturized structured light is expected in many application fields.A kind of structured vortex generators is proposed based on a metasurface consisting of rectangular nanoholes etched in a silver film,and the generated vortices with the same or different topological charges are distributed along the radial direction.The geometric metasurface is completed with the help of optical holography technology,and the structured vortex generator possesses high working efficiency and large information capacity.The proposed vortex generators work under circularly polarized light illumination,and the reproduced vortices of multiplexing vortex generator depend on the handedness of the circularly polarized light.This work paves a way to generate new structured light fields.The radially distributed vortices may be utilized to simultaneously screen or separate microparticles.The compact design of the structured vortex generator and the convenient switch of different structured vortices will be a benefit to expand the applications of structured vortex fields.

Edge enhancement of phase objects through complex media by using transmission-matrixbased spiral phase contrast imaging

The wavefront shaping based technique has been introduced to detect the edges of amplitude objects through complex media,but the extraction of the boundary information of invisible phase objects through complex media has not been demonstrated yet.Here,we present a phase contrast imaging technique to overcome the scattering,aiming to achieve the edge detection of the phase object through the complex media.An operator based on the experimentally measured transmission matrix is obtained by numerically adding a spiral phase in the Fourier domain.With the inverse of the filtered transmission matrix,we can directly reconstruct the edge enhanced images for both amplitude object and phase object beyond scattering.Experimentally,both digital and real objects are imaged,and the results verify that isotropic edge detection can be achieved with our technique.Our work could benefit the detection of invisible phase objects through complex media.