We report on the experimental observation of bound states of solitons in a graphene mode locked erbium doped fiber laser. By using graphene as a saturable absorber, we have obtained stable, single and bound soliton pulses, the latter with a full width at half maximum (FWHM) of 1.49 ps and a fixed pulse sep aration of 2.46 ps. Our results once again show that bound soliton pulses is an intrinsic feature of fiber lasers independent of the exact mode locking mechanism.

A tunable L-band dissipative soliton (DS) fiber laser with nonlinear polarization rotation (NPR) playing the roles of both a saturable absorber (SA) and a tunable filter has been demonstrated experimentally and numerically. By appropriate adjustment of the states of the polarization controllers (PCs) and the pump power, DSs with continuously tunable wavelengths have been observed over the wavelength range from 1583.0 to 1602.4 nm with a 3-dB spectral bandwidth of around 20 nm and from 1581.9 nm to 1602.6 nm with a 3-dB spectral bandwidth of around 4 nm. In addition, we have observed that by increasing the pump power, the 3-dB spectral bandwidth of the DS could be increased without pulse breaking. Numerical results for the characteristics of the DSs are in accord with the experimental data.

Pulse bursts with a controllable number of pulses per burst have been produced directly from a mode-locked Yb-doped fiber laser for the first time. Each output burst contained numerous pulses with a high pulse repetition rate of 29.4 MHz. The duration of a single pulse was 680 ps. The pulse burst had a repetition rate of 251.6 kHz. The pulse burst could easily be further amplified to a total pulse burst energy of ~795 nJ, corresponding to a total average power of 200 mW.

The generation and evolution processes of noise-like pulses (NLPs) in an all-normal-dispersion nonlinear polarization rotation (NPR) mode-locked Yb-doped fiber laser are numerically and experimentally investigated. We demonstrate that the amplitude modulation induced by reverse saturable absorption and the peak-power-limiting effect of the NPR plays a key role in the formation of fine-structure oscillations of NLPs. The width variation of the NLPs is also discussed in detail.

We propose and demonstrate an adjustable all-fiber comb filter with precisely controlled channel spacing by employing a tapered fiber in one arm of a Mach-Zehnder interferometer (MZI) for the first time. Using fused taper technology to draw the fiber, we can precisely control the optical path difference between the two arms of the MZI, thus realizing a precisely controllable channel spacing. By rotating the polarization controller state in the other arm of the MZI, the transmission spectrum wavelength can be continuously tuned. Comb filters with controllable channel spacings from 0.2 to 3.0 nm have been numerically studied and achieved in experiment. Applications of a filter based on a multi-wavelength tunable all-fiber laser source are also demonstrated.