Effect of Temperature and Germania on the Performance of Germania Doped Silica Fiber Raman Scattering Amplifier

The Raman gain coefficient, the attenuations at signal and pump wavelengths and the refractive indices of both core and cladding of silica doped Germania optical fiber are functions of the Germania ratio, temperature and wavelengths. The Raman amplifier gain increases with Germania ratio but it decreases with temperature. Also, Raman gain either increases or decreases with signal wavelength. As the fiber core radius increases, the Raman gain decreases. The gain distribution through the amplifier length of dual pumps with power divided ratio (S=0.5) is better than that for the forward pump amplifier and the backward pump amplifier. The forward pump has a maximized gain but the backward pump has a minimized gain, while the dual pumps have both the maximum and minimized gains. The final amplifier gain for the three kinds of pumps with the same pump power (Pp) is equally.The pump wavelength (λp=1.4553μm) gives the biggest Raman gain at the center of wideband signal wavelength (λs=1.50 to 1.60μm). With λp =1.48μm, the gain increases with λs until λs=1.57μm and after that the gain decreases with λs and so with the above three kinds of pumps, gain fluctuations over the band wavelength of signal. The threshold pump power and gain saturation are studied.

All-Fiber Optical Nonreciprocity Based on Parity-Time-Symmetric Fabry-Perot Resonators

Nonreciprocal light transmission in an all-fiber device with remotely tunable isolation ratio and switchable isolation direction is proposed and demonstrated. Three cascaded fiber Bragg gratings (FBGs) are inscribed in an erbium-ytterbium co-doped fiber (EYDF) to form two mutually coupled Fabry-Perot (FP) resonators. The two FP resonators have an identical geometry, but the gain and loss of the FP resonators, and their mutual coupling are manipulated by controlling the pumping power to realize broken parity-time (PT) symmetry. Strong optical nonreciprocity is achieved due to gain saturation nonlinearity that is enhanced by the broken PT symmetry. The proposed device is fabricated, and its operation is experimentally evaluated. Nonreciprocal light transmission with an isolation ratio of 8.58 dB at 1550 nm and a 3-dB bandwidth of 125 MHz is experimentally demonstrated. Our study also indicates, by optimizing the design, an isolation ratio up to 33 dB can be achieved. The proposed approach provides an all-fiber solution for a remotely tunable and optically controlled isolator, which may find great applications in software-defined optical networks.

THE INFLUENCES OF THE ASYMMETRIC GAIN SATURATION EFFECT ON THE DYNAMICS OF InGaAsP FABRY-PEROT LASERS

This paper reports on the influence of the asymmetric gain saturation on the dynamics of InGaAsP Fabry-Perot lasers. The results are obtained by numerical simulations of multimode rate equations. The gain saturation effects that results in competition phenomena among lasing modes are investigated. A hopping multimode case is examined in detail. With means of the bifurcation analysis the regions with instabilities in the evolution of the mode intensities have been found. The following operation in the plane of two parameters are obtained: stable single mode, stable multimode, bistabile, and multimode hopping. The pulse traces of amplitudes of modes are plotted to illustrate the observed behaviors. Finally, the influence of linewidth enhancement Henry factor on the laser behavior is investigated.

Controlling wave fronts with tunable disordered non-Hermitian multilayers

Unique and flexible properties of non-Hermitian photonic systems attract ever-increasing attention via delivering a whole bunch of novel optical effects and allowing for efficient tuning light-matter interactions on nano- and microscales. Together with an increasing demand for the fast and spatially compact methods of light governing, this peculiar approach paves a broad avenue to novel optical applications. Here, unifying the approaches of disordered metamaterials and non-Hermitian photonics, we propose a conceptually new and simple architecture driven by disordered loss-gain multilayers and, therefore, providing a powerful tool to control both the passage time and the wave-front shape of incident light with different switching times. For the first time we show the possibility to switch on and off kink formation by changing the level of disorder in the case of adiabatically raising wave fronts. At the same time, we deliver flexible tuning of the output intensity by using the nonlinear effect of loss and gain saturation. Since the disorder strength in our system can be conveniently controlled with the power of the external pump, our approach can be considered as a basis for different active photonic devices.

Мощность насыщения оптического усилителя на основе самоорганизующихся квантовых точек

Gain saturation in a semiconductor optical amplifier with an array of quantum dots was studied analytically and by numerical simulation on the basis of an analysis of the rate equations. It is shown that, at a moderate injection level, the saturation power increases in proportion to the current density, and then reaches its maximum value, limited by the rate of capture of charge carriers to the ground state and by the number of quantum dots interacting with photons. Expressions are proposed that allow an explicit description of the dependence of the saturation power on the current and its relationship with the internal parameters of the active region.