sheng Xiao

Observation of various bound solitons in a carbon-nanotube-based erbium fiber laser

Bound solitons with various phase differences and pulse separations were observed in a net-anomalous-dispersion erbium fiber laser mode-locked by carbon nanotubes, including two-soliton bound states with phase differences close to π (out of phase), 0 (in phase), and ±π/2, as well as triple-soliton bound states. To our knowledge, this is the first time that in-phase two-soliton bound states have been obtained experimentally in fiber lasers. Evolution of bound states with change of pump power was investigated, and stability of different bound states was compared. Mechanisms why and how various bound states appeared in the same fiber laser are discussed and analyzed.

The effect of surface treatments on hydrogen storage of carbon nanotubes

： Carbon nanotubes used in this experiment were grown from a acetylene－ hydrogen mixture on a support using different catalyst precursors. The surface characteristics of carbon nanotubes determined the interaction with hydrogen, so the materials thus produced were submitted to two different treatments, namely nitric acid and alkali solution to gain favorable adsorption surface, these treatments improved surface area and surface activity effectively. At last it can absorb 5％ of hydrogen at room temperature under 10 MPa, and the result is stable.

Broadband Graphene Saturable Absorber for Pulsed Fiber Lasers at 1, 1.5, and 2 μm

Ultrafast fiber lasers with broad spectral coverage are in great demand for a variety of applications, such as spectroscopy, and biomedical diagnosis. Graphene is an ideal ultrawide-band saturable absorber. We report broadband (up to ~1000 nm) ultrafast pulse generation from three fiber lasers mode-locked by a single graphene saturable absorber device. The mode-locked pulses were based on Yb-, Er- and Tm:Ho-doped fiber lasers at the central wavelength of 1035, 1564, and 1908 nm, respectively. The maximum output energy is up to 16.2 nJ at 1908 nm. It is the first time that ultrafast fiber lasers covering 1, 1.5, and 2 μm spectral region are mode-locked with a single graphene device. Our results validate the intrinsic broadband operation property of graphene devices for all major fiber laser wavelengths from 1 to 2 μm.

Analytical optimization of the net residual dispersion in SPM-limited dispersion-managed systems

Dispersion management is an effective technique to suppress the nonlinear impairment in fiber transmission systems, which includes tuning the amounts of precompensation, residual dispersion per span (RDPS), and net residual dispersion (NRD) of the systems. For self-phase modulation (SPM)-limited systems, optimizing the NRD is necessary because it can greatly improve the system performance. In this paper, an analytical method is presented to optimize NRD for SPM-limited dispersion-managed systems. The method is based on the correlation between the nonlinear impairment and the output pulse broadening of SPM-limited systems; therefore, dispersion-managed systems can be optimized through minimizing the output single-pulse broadening. A set of expressions is derived to calculate the output pulse broadening of the SPM-limited dispersion-managed system, from which the analytical result of optimal NRD is obtained. Furthermore, with the expressions of pulse broadening, how the nonlinear impairment depends on the amounts of precompensation and RDPS can be revealed conveniently.

Soliton rains in a normal dispersion fiber laser with dual-filter

We demonstrate an experimental observation of soliton rains in an all normal dispersion Yb-fiber laser. The cavity consists of a narrow bandwidth filter and a birefringent plate (BP) filter. Soliton rain is obtained in the weak mode-locking regime, while multisolitons behaving as soliton bunches and harmonic mode-locking under strong mode-locking are also observed. Distinctive multisoliton interactions are observed via changing the pump power and adjustment of the waveplates as well as the BP. To the best of our knowledge, this is the first demonstration of soliton rains in normal dispersion fiber lasers.

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.

Widely Spaced Bound States in a Soliton Fiber Laser With Graphene Saturable Absorber

Highly coherent two-soliton loosely bound states with pulse separation of two orders of magnitude of pulse width are generated by delicate control of initial conditions in a soliton fiber laser using a graphene mode-locker. It represents the most widely spaced bound state directly obtained in fiber lasers as far as overlap of two intracavity solitons is concerned.

Wavelength conversion of spectrum-sliced broadband amplified spontaneous emission light by hybrid four-wave mixing in highly nonlinear, dispersion-shifted fibers

We propose and demonstrate wavelength conversion of spectrum-sliced broadband amplified spontaneous emission light sources based on hybrid four-wave mixing (HFWM) in highly nonlinear, dispersion- shifted fibers (HNL-DSFs). The theory of HFWM between coherent pumps and incoherent signal is analyzed. The degenerate HFWM is demonstrated experimentally in a 1-km-long HNL-DSF, where the coherent pump light is provided by a tunable cw laser source and the incoherent signal light is spectrum-sliced from a broadband amplified spontaneous emission light source. A conversion efficiency of about -20.4 dB and a bandwidth of about 38 nm are measured. The experimental result agrees well with the theoretical analysis.

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.

Performance Evaluation of Tunable Channel-Selective Wavelength Shift by Cascaded Sum- and Difference-Frequency Generation in Periodically Poled Lithium Niobate Waveguides

We theoretically evaluate the performance of tunable channel-selective wavelength shift based on cascaded sum- and difference-frequency generation by the use of two pump lights in periodically poled lithium niobate waveguides. In double-pass configurations, the functions of wavelength add/drop and wavelength shift are easy to integrate in the same waveguide. Analysis shows that a longer waveguide more competently adapts narrower channel spacing in wavelength-division-multiplexed (WDM) systems. This wavelength shifter is flexible due to the almost separable operations of the two pumps: The channel is selected by setting the first pump, and the wavelength-shifting value is tuned by adjusting the second pump. This wavelength shifter has a very large dynamic region. For a 2.56-cm-long waveguide, the maximum dynamic region is as broad as 67 nm in a 0.4-nm channel-spacing WDM system. The dynamic region is mainly dominated by the limitation of multiple-channel crosstalk in a dense WDM system. However, it is dominated by the limitation of single-channel efficiency fluctuation in a coarse one