Effect Of Gain Dispersion Research Articles

Width-tunable pulse laser via optical injection induced gain modulation of semiconductor optical amplifiers

A width-tunable pulse laser via an optical injection induced gain modulation of a semiconductor optical amplifier (SOA) is demonstrated. When the pump current of the SOA is 330 mA or 400 mA and a continuous wave is injected into the laser cavity with different powers, bright or dark pulses with different pulse widths and frequency repetition rates are obtained. The bright and dark pulses are formed by the effect of gain dispersion and cross-gain modulation of the SOA.

Generation of single and multiple dissipative soliton in an erbium-doped fiber laser**Project supported by the National Natural Science Foundation of China (Grant No. 61505160).

We experimentally report on the generation of single and multiple dissipative soliton via nonlinear polarization rotation technique. The spectrum of the mode-locked dissipative soliton exhibits typical steep edges with a flat top; the pulse duration is 10.07 ps. It is found that with the pump power increasing from 110 mW to 161 mW, the top of the mode-locked spectrum becomes flater and the 3-dB spectral bandwidth is broadened, which indicates that the gain-dispersion effect is lowered under stronger pump. However, the full bandwidth of the spectrum is narrowed, which proves that the spectral filter effect increases and overcomes the effect of self-phase modulation induced spectral broadening. Such a phenomenon was not noticed nor reported before. Our experiment also demonstrates that the pulse interval is highly dependent on the input pump power: with pump power increasing, the pulse interval tends towards more uniform. So our observation qualitatively analyzes the relationship between mode-locked pulse characteristics and input pump power.

Generation of dark and bright pulses in an SOA-based Q-switched fiber laser

Bright and dark pulses in a Q-switched optical fiber laser based on a semiconductor optical amplifier were demonstrated. By changing the setting of the polarization controllers, bright or dark pulses with differing pulse widths and frequency repetition rates can be obtained. The bright pulse and dark pulse are formed mainly by the effect of gain dispersion of the semiconductor optical amplifier.

Dissipative vector soliton in a dispersion-managed fiber laser with normal dispersion.

We numerically study the vector dynamics of dissipative solitons (DSs) in a 2μm dispersion-managed fiber laser mode locked by a semiconductor saturable absorber mirror and operated in the normal dispersion regime. It is shown that the effective gain bandwidth is crucial for the DS generation. The steep spectral edges of DSs are the consequence of the interaction among the normal dispersion, fiber nonlinearity, gain and loss, and gain dispersion effect, etc. We numerically duplicate the experimental results and further explore the vector features of the generated DSs. Two DSs formed along the two orthogonal polarization directions which, incoherently coupled with each other, could propagate in the birefringent cavity with the same group velocity.

Comprehensive modelling of wave propagation in photonic devices

A simple and powerful modelling method in the time domain is established to resolve travelling waves inside photonic devices. The basic idea is to transform usual space–time coordinates (z, t) into a mixed grid (u, v) in which waves propagate along their characteristic lines, resulting in an inherent numerical stability, as well as easy interpretation of all parametric variables and their derivatives. In this study, the authors will demonstrate, for the first time, how the effect of gain dispersion can be dealt with using an efficient fourth-order algorithm, which attains high precision, high speed as well as very large stepsize. Excellent agreement with existing analytical results is obtained.

Study of the gain saturation effect on the propagation of dark soliton in Er + 3 -doped, Ga 5Ge 20Sb 10S 65 chalcogenide fiber amplifier

We study the effect of gain saturation on the propagation of fundamental dark soliton in a nonlinear, dispersive and amplifying medium. The Er + 3 -doped, Ga 5Ge 20Sb 10S 65 chalcogenide glass is used for dark and erbium doped silicon glass for bright solitons. The numerical simulations show that dark soliton doesn't split to subpulses unlike bright soliton and also the dark soliton is more stable in the presence of gain saturation and gain dispersion effects. So the chalcogenide glasses are suitable for designing all optical devices.

Analytical study of pulse amplification in silicon Raman amplifiers

The nonlinear process of stimulated Raman scattering is important for silicon photonics as it enables optical amplification and lasing. To understand the dynamics of silicon Raman amplifiers (SRAs), a numerical approach is generally employed, even though it provides little insight into the contribution of different SRA parameters to the signal amplification process. In this paper, we solve the coupled pump-signal equations analytically under realistic conditions, and derive an exact formula for the envelope of a signal pulse when picosecond optical pulses are amplified inside a SRA pumped by a continuous-wave laser beam. Our solution is valid for an arbitrary pulse shape and fully accounts for the Raman gain-dispersion effects, including temporal broadening and group-velocity reduction (a slow-light effect). It can be applied to any pumping scenario and leads to a simple analytic expression for the maximum optical delay produced by the Raman dispersion in a unidirectionally pumped SRA. We employ our analytical formulation to study the evolution of optical pulses with Gaussian, exponential, and Lorentzian shapes. The ability of a Gaussian pulse to maintain its shape through the amplifier makes it possible to realize soliton-like propagation of chirped Gaussian pulses in SRAs. We obtain analytical expressions for the required linear chirp and temporal width of a soliton-like pulse in terms of the net signal gain and the Raman-dispersion parameter. Our results are useful for optimizing the performance of SRAs and for engineering controllable signal delays.

Gain dispersion for dissipative soliton generation in all-normal-dispersion fiber lasers

Properties of dissipative solitons generated in all-normal-dispersion fiber lasers through the gain dispersion effect are numerically studied by using a pulse-tracing technique that considers interaction between gain saturation, gain dispersion, cavity dispersion, fiber Kerr nonlinearity, and cavity boundary conditions. The numerical results qualitatively match with experimental observations and show that the finite gain bandwidth, together with the pump power, determines the properties of the generated dissipative solitons, which further dictates the performance of the pulse compression.

Self-similar parabolic pulses in optical fiber amplifiers with gain dispersion and gain saturation

The generation and propagation of an asymptotic parabolic pulse in an optical fiber amplifier with the gain dispersion effect and gain saturation effect is studied. It is found that initial input pulses with small amplitudes and widths can evolve into self-similar pulses at the asymptotic limit. The central region of the self-similar pulse is described by the invert parabola, and its width and power increase linearly, but with its peak amplitude and the width of its spectrum, remain constant. The parameter region for the existence of the parabolic pulse is given.

Effect of two photon absorption on nonlinear pulse propagation in gain medium

The effects of two photon absorption (TPA) and gain dispersion on soliton propagation in amplified medium are investigated. For finite gain bandwidth, the effect of gain dispersion becomes significant along with TPA and is treated as perturbation in fundamental soliton propagation. Including these perturbing effects an analytical expression of integrated intensity is formulated applying a completely new methodology by adopting Rayleigh’s dissipation function in the framework of variational approach. With classical analogy, the Euler–Lagrange equation in non-conservative system is used to solve the problem analytically. In order to justify the analytical prediction a numerical verification is made by split-step beam propagation method following Ginzburg–Landau equation.

이득 분산이 다중 영역 복소 결합 DFB 레이저의 Self-Pulsation 특성에 미치는 효과

이득 분산이 두 개의 복소 결합 DFB 영역과 위상조정 영역으로 구성되는 다중 영역 복소 결합 DFB 레이저에서 발진하는 두 모드의 비팅에 의한 self-pulsation (SP) 주파수와 출력 파워의 변조지수에 미치는 영향에 대하여 살펴보았다. 능동 영역의 이득이 최대가 되는 파장을 두 DFB 영역의 발진 모드의 파장 중심 또는 브래그 파장 중심에 위치시킨 경우가 특정 DFB 영역의 발진 모드의 파장 또는 브래그 파장에 위치시킨 경우에 비하여 두 DFB 영역의 브래그 파장 차이, <TEX>${\Dalta}{\lambda}_{B}$</TEX>, 증가에 따른 두 발진 모드가 받는 이득 차이가 적게 발생하여 최대 SP 주파수가 크고, 변조지수 특성도 좋음을 볼 수 있었다. 또한 능동 영역의 이득이 최대가 되는 파장을 두 DFB 영역의 브래그 파장 중심에 위치시키는 경우가 발진 모드의 파장 중심에 위치시키는 경우에 비하여 더 큰 최대 SP 주파수를 얻을 수 있었고 변조지수 특성도 더 우수함을 볼 수 있었다. The effect of gain dispersion on the self-pulsation (SP) characteristics due to the mode beating of two modes emitted in a multisection DFB laser composed of two complex-coupled DFB sections and a phase control section is investigated. When the peak wavelength, <TEX>${\lambda}_{p}$</TEX>, of the gain spectrum of the DFB section is positioned in the center of the lasing wavelengths or the Bragg wavelengths of the two DFB sections, the maximum SP frequencies are higher and the modulation index has better characteristics compared to those cases for <TEX>${\lambda}_{p}$</TEX> fixed at the lasing wavelength or Bragg wavelength of one DFB section, when the difference between the Bragg wavelengths of the two DFB sections, <TEX>${\Dalta}{\lambda}_{B}$</TEX>, is varied. When <TEX>${\lambda}_{p}$</TEX> is positioned in the renter of the Bragg wavelengths of the two DFB sections, the maximum SP frequency is higher and of the modulation index has better characteristics compared to those of the case for <TEX>${\lambda}_{p}$</TEX> positioned in the center of the lasing wavelengths of the two DFB sections.

Picosecond soliton transmission by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors

Stable picosecond soliton transmission is demonstrated numerically by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors (NALMs). We show that, as compared with previous soliton transmission schemes that use conventional NALMs or nonlinear optical loop mirror and amplifier combinations, the present scheme permits a significant increase of loop-mirror (amplifier) spacing. The broad switching window of the present device and the high-quality pulses switched from it provide a reasonable stability range for soliton transmission. We also show that a soliton self-frequency shift can be suppressed by the gain-dispersion effect in the amplifying fiber loop and that soliton-soliton interactions can be partially reduced by using lowly dispersive transmission fibers.

Simulation of high-power pulse generation due to modelocking in long multisection lasers

The dynamic behaviour of long monolithic modelocked lasers for the emission wavelength 1.06 /spl mu/m containing an active gain section and a passive cavity section was simulated. Numerical tools have been used to solve the travelling wave and carrier rate equations taking into account the effect of gain dispersion. Different configurations and arrangements including an absorber section and a section with a DBR were studied and compared. Best pulses are achieved with a configuration having a saturable-absorber section at the front facet. Peak powers of more than 5 W, pulse energies greater then 15 pJ and time-bandwidth products less than 0.5 are obtained by optimising the resonator configuration.

Gain dispersion and saturation effects in four-wave mixing in semiconductor laser amplifiers

This paper addresses four-wave mixing (FWM) in semiconductor laser amplifiers from the point of view of a propagation problem. The gain dispersion effect, i.e., the difference of the gain factors for the pump, probe and signal waves is shown to be significant in the case of large detunings >1 THz. It is given an analytical solution of the FWM problem including gain dispersion and saturation effects. Considering the saturation behaviour, it is shown that the linear gain factors for the different waves and the nonlinear susceptibilities associated with the different nonlinear effects must be characterized by different carrier densities at transparency. A comparison of our theory with a numerical model, with previous approaches and with experimental data is given.

Effect of gain dispersion on ultrashort pulse amplification in semiconductor laser amplifiers

The effect of gain dispersion in semiconductor laser amplifiers is discussed by considering an amplifier model that includes both gain saturation and gain dispersion. The saturated and unsaturated amplification regimes corresponding to whether the pulse energy is comparable to or much smaller than the saturation energy, are discussed separately. In the unsaturated regime, gain-induced group-velocity dispersion is found to play an important role. The amplified pulse can be compressed or broadened depending on whether the input pulse is chirped or unchirped. The pulse spectrum remains largely unaffected in the linear regime. In the saturation regime, self-phase modulation leads to considerable changes in the pulse spectrum. >

Effect of gain dispersion and stimulated Raman scattering on soliton amplification in fiber amplifiers

Amplification of ultrashort solitons in fiber amplifiers is discussed by considering a general model that includes gain saturation, gain dispersion, and intrapulse stimulated Raman scattering. The numerical results show that an interplay between gain dispersion and intrapulse Raman scattering can lead to novel temporal and spectral features. Under high-gain conditions the input pulse is found to split into several subpulses propagating at different speeds. Each subpulse evolves toward a chirped soliton whose width is governed by the gain bandwidth and is ~50 fsec for erbium-doped fiber amplifiers.

Carrier-induced group-velocity dispersion and pulse compression in semiconductor laser amplifiers

The effect of gain dispersion on pulse amplification in semiconductor laser amplifiers is investigated theoretically. A novel phenomenon, referred to as carrier-induced group-velocity dispersion, is shown to influence considerably the amplified pulse. Chirped input pulses are predicted to be compressed in the presence of carrier-induced dispersion even when the amplifier operates far below saturation. The dependence of the compression factor on device parameters such as the pulse width, the amplifier gain, and the linewidth enhancement factor are studied using a simple analytic model. The results are important for optical communication systems as they imply that semiconductor laser amplifiers can be used to compensate simultaneously for the effects of both fibre loss and fibre dispersion when used as in-line amplifiers. >

Generation of short pulses of coherent electromagnetic radiation in a free-electron laser amplifier

Theoretical and experimental studies of the evolution of a frequency-chirped pulse under the influence of both phase and gain dispersion effects induced by the free-electron laser interaction are presented. For the experimental parameters used (electron beam voltage V=150 kV, wiggler periodicity l/sub w/=3.5 cm, gain approximately 10 dB, input pulse width Delta t approximately 200 ns, frequency w/sub 0//2 pi =10 GHz, and frequency chirp alpha /2 pi approximately 5 MHz/ns), pulses of a few nanoseconds were generated after an interaction length of 2.30 m, in good agreement with theoretical expectations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>