Mohamed A. Abdelalim

Steady and oscillating multiple dissipative solitons in normal-dispersion mode-locked Yb-doped fiber laser.

Multiple dissipative solitons are numerically studied in the normal-cavity-dispersion Yb-doped fiber laser. Soliton pairs and triplets of different types are found in parameter domain where single soliton mode-locking is unstable. Similar scenario is found for soliton pair and triplet: an additional weak soliton supplements already existing solitons, then with increasing gain the solitons start oscillating and at higher gain the soliton complex becomes stable. Spectral profiles of the solitons dynamically change taking either parabolic-like or Pi-like or M-like shape similar to those described in the literature for individual dissipative soliton at different pump level.

Generalized Analytical Model for Dissipative Soliton in All-Normal-Dispersion Mode-Locked Fiber Laser

The spectral filter bandwidth plays a crucial role in the pulse formation in all-normal-dispersion fiber lasers. It is affected by the parameters of the mode locker in the laser cavity. In this paper, a modified analytical model is developed and used to study the dependence of the spectral bandwidth on the small signal absorption, and the saturation power of a lumped saturable absorber. A comparison among the proposed analytical model results, numerical calculations, and experimental measurements shows a very good agreement.

An Efficient Semi-Vectorial Model for All-Fiber Mode-Locked Femtosecond Lasers Based on Nonlinear Polarization Rotation

A novel closed form equation to model nonlinear polarization evolution based mode-locking in femtosecond fiber lasers is presented. A comparison with the full-vectorial model demonstrates the accuracy of the presented model. The new method takes less than 5% of the time needed by the full-vectorial method for the same computational platform. The comparison with the experimental results shows an excellent agreement with the new models results.

Effect of mode locking technique on the filtering bandwidth limitation in all normal dispersion femtosecond fiber laser

The dependence of the filtering bandwidth on the mode locking technique was studied in details in two types of mode locked fiber laser cavities; one utilizes SESAM, while the other employs NPE. The results show that for the two cases, below certain value of filtering bandwidth, no mode locking can be observed and the cavities will be in a lossy region. Moreover, NPE-based all fiber cavities can support narrower spectral bandwidth compared to SESAM-based cavities. Hence, NPE-based cavities produce shorter pulse width than SESAM-based ones. Experimental investigation was carried out to verify our simulation results and good agreement was achieved.

Effect of narrow spectral filter position on the characteristics of active similariton mode-locked femtosecond fiber laser

A significant change in active similariton characteristics, both numerically and experimentally, is observed as a function of the location of the lumped spectral filter. The closer the spectral filter is to the input of the Yb(3+)-doped fiber, the shorter the de-chirped pulse width. The peak power of the de-chirped pulse has its maximum value at a certain location of the spectral filter. Four different positions of the spectral filter inside the laser cavity have been theoretically studied and two of them have been verified experimentally.

Peak Power Optimization of Optical Pulses Using Low-Doped Gain-Medium in Femtosecond Fiber Laser

We have investigated both theoretically and experimentally a method to increase the peak power in femto-second fiber laser by using a low-doped long-length gain medium. The accumulated nonlinear phase shift as well as its threshold value for single pulse operation was studied and used to explain the robustness of such cavity against multipulsing and optical wave breaking.

Increasing energy in an ytterbium femtosecond fiber laser with a longer gain medium and lower doping

An increase in energy of pulses generated in a similariton mode-locked femtosecond fiber laser is shown experimentally by increasing the length while reducing the doping of the ytterbium-doped fiber gain medium. Mode-locking is achieved by nonlinear polarization rotation evolution in a cavity using a combination of fiber and bulk optical components. The level of doping of the gain medium is varied by using lengths of differently doped ytterbium fiber. Experimental results verify that an increase in length of gain medium with a lower doping results in an increase in the output pulse energy.