Mingshan Li

All-fiber passively mode-locked thulium-doped fiber ring laser using optically deposited graphene saturable absorbers

An all-fiber passively mode-locked thulium-doped fiber ring oscillator is constructed using optically deposited few layer graphene micro-sheets as the saturable absorber (SA). The mode-lock operation was achieved by 130-mW pump power at 1.5-μm. The fiber oscillator produces 2.1-ps soliton pulse output with 80-pJ per pulse energy. The 3-dB bandwidth of the laser output was measured as 2.2-nm. The RF signal-to-noise ratio of 50-dB and sub 20-Hz 3-dB bandwidth of the laser output confirms the stable laser operation with low time jittering. This paper shows that graphene can be an effective saturable absorber for the development of mid-IR fiber mode-locked laser.

All-fiber ultrafast thulium-doped fiber ring laser with dissipative soliton and noise-like output in normal dispersion by single-wall carbon nanotubes

An ultrafast thulium-doped fiber laser with large net normal dispersion has been developed to produce dissipative soliton and noise-like outputs at 1.9 μm. The mode-locked operation was enabled by using single-wall carbon nanotubes as saturable absorber for all-fiber configuration. Dissipative soliton in normal dispersion produced by the fiber laser oscillator was centered at 1947 nm with 4.1-nm FWHM bandwidth and 0.45 nJ/pulse. The output dissipative soliton pulses were compressed to 2.3 ps outside the laser cavity.

Regenerated distributed Bragg reflector fiber lasers for high-temperature operation.

This Letter presents distributed Bragg reflector (DBR) fiber lasers for high-temperature operation at 750°C. Thermally regenerated fiber gratings were used as the feedback elements to construct an erbium-doped DBR fiber laser. The output power of the fiber laser can reach 1 mW at all operating temperatures. The output power fluctuation tested at 750°C was 1.06% over a period of 7 hours. The thermal regeneration grating fabrication process opens new possibilities to design and to implement fiber laser sensors for extreme environments.

Flexible photonic components in glass substrates.

This paper demonstrates the fabrication and measurements of flexible photonic lightwave circuits in glass substrates. Using temporally and spatially shaped ultrafast laser pulses, highly symmetrical and low-loss optical waveguides were written in flexible glass substrates with thicknesses ranging from 25 µm to 100 µm. The waveguide propagation loss, measured by optical frequency domain reflectometry, was 0.11 dB/cm at 1550 nm telecommunication wavelength. The bend loss of the waveguide is negligible at a radius of curvature of 1.5 cm or greater. Additionally, the waveguides are thermally stable up to 400°C. This paper presents alternatives to fabricating flexible photonics in traditionally used polymeric materials.

Nonlinear lightwave circuits in chalcogenide glasses fabricated by ultrafast laser

This Letter reports a nonlinear directional waveguide coupler written by ultrafast laser in gallium lanthanum sulfide chalcogenide glass. The nonlinear waveguide device is tested with laser pulses input in two orthogonal polarizations, and all optical switching at 1040 nm between the two coupled waveguides is observed at a peak fluence of 16 GW/cm2. The spectra and autocorrelation measurement from the waveguide outputs show dominant nonlinear effects and negligible dispersion for light propagation in both channels.

Ultrafast Laser Fabrication of 3D Photonic Components in Flexible Glasses

We demonstrated the first flexible photonics lightwave circuits in glasses. The waveguide was written in ≤100μm thick Corning® Willow® Glass by a spatially and temporally shaped femtosecond ultrafast laser beam with processing speed up to 50mm/s. The flexible glass waveguide shows superior loss performance of 0.11dB/cm at λ=1550nm, with negligible bending loss down to a radius of 6.7cm.

Passively Q-switched thulium-doped fiber laser by graphene saturable absorber

A graphene-based saturable absorber was fabricated by optically depositing layers of graphene onto the end tip of single mode fiber, and it was used to passively Q-switch thulium-doped fiber laser at 2 μm pumped by EDFA. The spectrum of the graphene Q-switched thulium-doped fiber laser and the relationship between the output power, repetition rate and pump strength are studied and presented.

Noncircular Refractive Index Profile and Breakdown of Mode Degeneracy of Vertical Cavity Surface Emitting Lasers

Spatially and spectrally resolved near-field images of the transverse mode patterns of vertical cavity surface emitting lasers (VCSELs) are obtained by confocal microscopy with optical spectrum analyzer. A non-circular internal effective index profile of the VCSEL is inferred from the observed wavelength splitting of the degenerated modes. Using the mode intensity patterns associated with their spectral information, an elliptical parabolic profile superposed to a step-like refractive index profile is extracted by fitting the internal structural parameters of VCSEL. Wavelength splitting of the degenerated LG01 modes is calculated from the fitting results, and is found to be in reasonable accord with our experiment results.

Optical Switching by Nonlinear Lightwave Circuits Inscribed in Chalcogenide Glass by Ultrafast Laser

We report nonlinear lightwave circuits inscribed in chalcogenide glass by ultrafast laser. Exploiting the large nonlinearity of the material, optical switching is demonstrated with reduced power in 1D waveguide array and waveguide Bragg grating.

Nonlinear optical localization in embedded chalcogenide waveguide arrays

We report the nonlinear optical localization in an embedded waveguide array fabricated in chalcogenide glass. The array, which consists of seven waveguides with circularly symmetric cross sections, is realized by ultrafast laser writing. Light propagation in the chalcogenide waveguide array is studied with near infrared laser pulses centered at 1040 nm. The peak intensity required for nonlinear localization for the 1-cm long waveguide array was 35.1 GW/cm2, using 10-nJ pulses with 300-fs pulse width, which is 70 times lower than that reported in fused silica waveguide arrays and with over 7 times shorter interaction distance. Results reported in this paper demonstrated that ultrafast laser writing is a viable tool to produce 3D all-optical switching waveguide circuits in chalcogenide glass.