Hussein E. Kotb

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.

MEMS-based Fourier transform spectrometer using pulsed infrared light source

MEMS-based FTIR spectrometers are good candidates for handheld and IoT applications due to their high speed of operation, ultra-compact size and low cost. Light sources used for FTIR spectroscopy are usually limited to thermal light sources that continuously emit black body radiation. However, the use of pulsed sources has many advantages, such as reducing detector noise and enabling new kinds of spectroscopy measurements that depend on pulsed sources such as supercontinuum sources and non-linear infrared spectroscopy. The use of these pulsed sources with the high-speed MEMS is, thus, of great interest. In this work, we study the effect of using a pulsed IR source with a MEMS FTIR spectrometer on the obtained spectrum. The system is analyzed for different operation regimes from quasi-static to high-speed pulses for different duty cycles and repetition rates. Two measurement setups are used. The first involves using pulsed white light output from a thermal source with an optical chopper. The chopper frequency is changed from 20 Hz to 1 kHz at duty cycle values from 1% to 50%. The second setup uses an acousto-optic modulator to square-wave modulate the amplified spontaneous emission of a semiconductor optical amplifier with a repetition rate ranging from 20 Hz to 2 MHz and duty cycle values from 5% to 50%. Degradation in signal-to-noise ratio as well as spectral distortion are analyzed for different regimes of operation.

Narrow line width dual wavelength semiconductor optical amplifier based random fiber laser

A novel narrow line-width Single longitudinal mode (SLM) dual wavelength random fiber laser of 20 nm separation between wavelengths of 1530 and 1550 nm is presented. The laser is based on Rayleigh backscattering in a standard single mode fiber of 2 Km length as distributed mirrors, and a semiconductor optical amplifier (SOA) as the optical amplification medium. Two optical bandpass filters are used for the two wavelengths selectivity, and two Faraday Rotator mirrors are used to stabilize the two lasing wavelengths against fiber random birefringence. The optical signal to noise ratio (OSNR) was measured to be 38 dB. The line-width of the laser was measured to be 13.3 and 14 KHz at 1530 and 1550 nm respectively, at SOA pump current of 370 mA.

Narrow line width semiconductor optical amplifier based random laser

We report a novel narrow line width single longitudinal mode random laser at wavelength of 1550 nm. The laser is based on Rayleigh backscattering in a standard single mode fiber (SMF-28e) as a distributed mirror [1,2], and the semiconductor optical amplifier (SOA) as the gain medium. The optical signal to noise ratio was measured to be 34 dB. The line width of the laser was observed to be monotonically increasing with SOA bias current. The minimum line width of the laser was measured to be 6.5 KHz at SOA current of 170 mA. The maximum value of optical power was measured to be 4 mW.

Dual wavelength SOA based fiber ring laser

In this paper we present a novel dual wavelength SOA based fiber ring laser. The ring laser combines the effect of SOA gain starving at the edge of the gain spectrum and the polarization state in the PM fiber ring to generate a dual wavelength laser at 1452.7 nm and 1454.5 nm with single mode operation verified. With the proposed technique, single wavelength single mode laser operation can be easily obtained by adjusting the SOA pumping current and the ring polarization state.