S. V. Popov

Tm-doped fiber laser mode-locked by graphene-polymer composite

We demonstrate mode-locking of a thulium-doped fiber laser operating at 1.94 μm, using a graphene-polymer based saturable absorber. The laser outputs 3.6 ps pulses, with ~0.4 nJ energy and an amplitude fluctuation ~0.5%, at 6.46 MHz. This is a simple, low-cost, stable and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics.

Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS₂).

We fabricate a few-layer molybdenum disulfide (MoS₂) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 μs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS₂ sample, despite operating at photon energies lower than the material bandgap.

Visible supercontinuum generation in photonic crystal fibers with a 400W continuous wave fiber laser

We demonstrate continuous wave supercontinuum generation extending to the visible spectral region by pumping photonic crystal fibers at 1.07 microm with a 400 W single mode, continuous wave, ytterbium fiber laser. The continuum spans over 1300 nm with average powers up to 50 W and spectral power densities over 50 mW/nm. Numerical modeling and understanding of the physical mechanisms has led us to identify the dominant contribution to the short wavelength extension to be trapping and scattering of dispersive waves by high energy solitons.

Watts-level frequency doubling of a narrow line linearly polarized Raman fiber laser to 589 nm

A single-mode, linearly polarized, 1118 nm ytterbium fiber laser was applied to pumping of a short fiber length, polarization-maintaining Raman cavity, resulting in a 0.4 nm linewidth, 23 W CW source at 1179 nm. Efficient, single-pass frequency doubling of the Raman source in MgO doped PPLN to 589 nm was demonstrated with CW power levels in excess of 3 W. No beam quality degradation was observed due to photorefraction at pump power densities up to 2 MW/cm(2). The proposed approach can be readily extended to Watt-level generation of any desired wavelength in the 560 to 770 nm range.

Solution processed MoS2-PVA composite for sub-bandgap mode-locking of a wideband tunable ultrafast er:fiber laser

We fabricate a free-standing few-layer molybdenum disulfide (MoS2)-polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a wideband tunable, ultrafast mode-locked fiber laser. Stable, picosecond pulses, tunable from 1,535 nm to 1,565 nm, are generated, corresponding to photon energies below the MoS2 material bandgap. These results contribute to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.

Continuous-wave, high-power, Raman continuum generation in holey fibers

The possibility of using low pump power for cw Raman continuum generation is demonstrated by optimization of the pump peak power and by accounting for the loss-related reduction of the effective length of Raman interaction in holey fibers. A 3.8-W, 324-nm-wide cw Raman continuum with a spectral power density higher than 10 mW/nm is generated in a completely fiber-integrated, single-mode format.

Nanosecond-pulse fiber lasers mode-locked with nanotubes

We demonstrate that mode-locking of ytterbium fiber lasers with a carbon nanotube saturable absorber can produce pulses ranging from 20 ps to 2 ns at repetition rates between 21 MHz and 177 kHz, respectively, depending on cavity length. Nonlinear polarization evolution is not responsible for mode-locking. Even in the nanosecond regime, clean single pulses are observed and the pulse train exhibits low jitter. Combined with extremely large chirp, these properties are suited for chirped-pulse amplification systems.

29 W High power CW supercontinuum source.

A 29 W CW supercontinuum spanning from 1.06 to 1.67 microm is generated in a short length of PCF with two zero dispersion wavelengths. The continuum has the highest spectral power density, greater than 50 mW/nm up to 1.4 microm, reported to date. The use of a short length of PCF enables the continuum to expand beyond the water loss at 1.4 microm. The dynamics of the continuum evolution are studied experimentally and numerically with close attention given to the effects of the water loss and the second zero dispersion wavelength.

Extended blue supercontinuum generation in cascaded holey fibers

By combining multiple photonic crystal fibers with sequentially decreasing zero-dispersion wavelengths we have produced a 1.2 W average-power white-light continuum, covering the visible-near-infrared spectrum from 0.44 to 1.89 microm (10 dB width), with an all-fiber picosecond ytterbium pump laser. Wavelengths as short as the ultraviolet (0.35 microm), and spectral power densities of more than 2 mW/nm in the blue spectral region, have been generated. The process is understood in terms of optimizing four-wave mixing phase matching to enhance short-wavelength generation.

Generation and direct measurement of giant chirp in a passively mode-locked laser.

We evaluate the shape and chirp of nanosecond pulses from a fiber laser passively mode locked with a nanotube-based saturable absorber by using a synchronously scanning streak camera and a monochromator to directly measure the pulse spectrogram. We show that the stable sech(2) output pulse possesses a predominantly linear chirp, with a residual quartic phase and low noise. Comparison with analytical mode-locking theory shows a good quantitative agreement with the master equation mode-locking model.