Amplification Of Ultrashort Optical Pulses Research Articles

Amplification of ultra-short optical pulses in a two-pump fiber optical parametric chirped pulse amplifier

We demonstrate with realistic numerical simulations that fiber optical parametric chirped pulse amplification is able to amplify ultra-short optical pulses. Such amplifiers driven by two-pump waves can amplify pulse bandwidth twice as large as the one of a single pump configuration. We show that pulses as short as 50 fs can be directly amplified. In addition, we take benefit from the saturation regime to achieve spectral broadening which makes possible to reduce pulse duration down to 15 fs.

Impact of pumping configuration on all-fibred femtosecond chirped pulse amplification

We experimentally compared the co- and counter-propagative pumping scheme for the amplification of ultra-short optical pulses. According to pumping direction we show that optical pulses with a duration of 75 fs and 100mW of average output power can be obtained for co-propagative pumping, while pulse duration is never shorter than 400 fs for the counter-propagative case. We show that the impact of non-linear effects on pulse propagation is different for the two pumping configurations. We assume that Self Phase Modulation (SPM) is the main effect in the copropagative case, whereas the impact of Stimulated Raman Scattering is bigger for the counter-propagative case.

Divided-pulse amplification of ultrashort pulses

We propose and demonstrate a new approach, to the best of our knowledge, for avoiding nonlinear effects in the amplification of ultrashort optical pulses. The initial pulse is divided longitudinally into a sequence of lower-energy pulses that are otherwise identical to the original, except for the polarization. The low-intensity pulses are amplified and then recombined to create a final intense pulse. This divided-pulse amplification complements techniques based on dispersion management.

Saturation behavior and self-phase modulation of picosecond pulses in single-stripe and tapered semiconductor laser amplifiers

We experimentally investigate and theoretically describe the amplification of ultrashort optical pulses in a double-stage InGaAs-semiconductor laser amplifier system consisting of a double-pass single-stripe diode laser and a tapered amplifier. The pulses were generated by a mode-locked single-stripe laser in an external-resonator configuration. On amplification in a tapered amplifier, pulses exhibited both spectral broadening and distortion, depending on the tapered amplifier current and the injected optical pulse power. This behavior originates from the dynamic nonlinear carrier induced spatiospectral gain and index changes as well as gain saturation and leads to self-phase modulation. The origin of the observed behavior is revealed by a spatially resolved microscopic theory based on Maxwell–Bloch–Langevin equations that takes into account many-body interactions, energy transfer between carrier and phonon systems, and, in particular, the spatiotemporal interplay of stimulated and amplified spontaneous emission and noise.

Parametric gain of the generation and the amplification of ultrashort optical pulses

A theoretical model for calculating the effective gain of parametric generation and amplification of ultrashort optical pulses is presented. This model takes into account both spatial and temporal effects, including spatial beam broadening, temporal pulse broadening, spatial walk-off of the pulse beams, and temporal walk-off of the parametrically interacting pulses. An analytical formulation for the parametric efficiency coefficient and the effective gain in terms of six spatial and temporal characteristic lengths is obtained. This formulation allows for an easy evaluation of the threshold and the efficiency of a synchronously pumped optical parametric oscillator generating ultrashort pulses without requiring the solution of a differential equation. It can also be used to calculate the amplification factor and the output pulse energy in parametric amplification and difference-frequency generation of ultrashort pulses. Numerical results for picosecond and femtosecond optical parametric generation and amplification in the KTP crystal are presented for many different experimental conditions.

Effect of two-photon absorption on the amplification of ultrashort optical pulses.

The effect of two-photon absorption on the amplification of ultrashort optical pulses is studied theoretically by solving a generalized nonlinear Schrodinger equation. An input pulse can be simultaneously amplified and compressed, although the compression factor is smaller in the presence of two-photon absorption. The amplified pulse evolves toward a chirped soliton that is the solitary-wave solution of the underlying propagation equation. It can split into several chirped solitons whose number, width, and peak power depend on the amplifier parameters

A highly efficient two-stage Er/sup 3+/-doped optical fiber amplifier employing an optical gate to effectively reduce ASE

Highly efficient amplification of ultrashort optical pulses is demonstrated with a two-stage Er/sup 3+/-doped optical fiber amplifier that includes an optical gate to efficiently reduce amplified spontaneous emission (ASE) generated from the first Er/sup 3+/-doped fiber. A gain of 49 dB, an amplified peak power 0f 105 W, and 1.05 nJ pulse energy are achieved for 2-Mb/s, 10-ps pulses at a total pumping power of 90 mW from 1.48- mu m LDs. >

Self-phase modulation and spectral broadening of optical pulses in semiconductor laser amplifiers

Amplification of ultrashort optical pulses in semiconductor laser amplifiers is shown to result in considerable spectral broadening and distortion as a result of the nonlinear phenomenon of self-phase modulation (SPM). The physical mechanism behind SPM is gain saturation, which leads to intensity-dependent changes in the refractive index in response to variations in the carrier density. The effect of the shape and the initial frequency chirp of input pulses on the shape and the spectrum of amplified pulses is discussed in detail. Particular attention is paid to the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives. The experimental results, performed by using picosecond input pulses from a 1.52- mu m mode-locked semiconductor laser, are in agreement with the theory. When the amplified pulse is passed through a fiber, it is initially compressed because of the frequency chirp imposed on it by the amplifier. This feature can be used to compensate for fiber dispersion in optical communication systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Formation and amplification of ultrashort optical pulses as a result of stimulated scattering in opposite directions

It is shown that the growth and contraction of a Stokes pulse formed as a result of stimulated Brillouin scattering are not limited by the hypersound relaxation time Tr (or, in the case of stimulated Raman scattering in opposite directions, by the transverse relaxation time T2). Amplification of a pulse of duration Ts < Tr is analogous to the propagation of a transient π pulse in a two-level laser amplifier. In a long stimulated-scattering amplifier a Stokes pulse always assumes a quasiself-similar profile which retains memory only of the leading edge of the input pulse; during propagation this pulse collects all the pump radiation energy and contracts so that its area remains constant and approximately equal to π/2. A study is made of the conditions under which such pulses form from spontaneous noise and it is demonstrated that a high degree of reduction of the pump pulse duration is possible in the course of stimulated Brillouin scattering in rare gases and this may be accompanied by an increase in the power by a factor of the order of 102.

Generation and amplification of ultrashort optical pulses

During the last two years since the 1966 Iternational Quantum Electronics Conference further progress toward obtaining high-power light pulses has taken place. An effective method of ultrashort light pulse generation (mode locking) has been developed, further development of the method of coherent amplification of light pulses has been recorded, and new prospective ideas have been put forward. The present paper briefly reports on the data obtained by us in these directions.