Chirp Dependence Research Articles

Effects of filtering on Gordon–Haus timing jitter in dispersion-managed systems

The effects of filtering on the Gordon–Haus timing jitter of chirped optical pulses in dispersion-managed communication systems with lumped and distributed amplification are studied in detail. Evolution equations for the average frequency and time delay are derived and solved analytically. Distributed amplification produces less timing jitter than lumped amplification. For short distances the timing jitter depends explicitly on the chirp, whereas for long distances it does not. The implicit chirp dependence that remains is inherited from the soliton energy. Simple formulas are derived for the asymptotic rates at which timing jitter grows. Numerical examples are described for 10-Gb/s systems and their relevance to 40-Gb/s systems is discussed. Although filtering limits the timing jitter in dispersion-managed systems, it precludes the reduction of timing jitter by dispersion postcompensation.

Klystron instability of a relativistic electron beam in a bunch compressor

In this paper, we consider a klystron-like mechanism of amplification of parasitic density modulations in an electron bunch passing a magnetic bunch compressor. Analytical expressions are derived for the small-signal gain. The effect of wakefields in front of the bunch compressor is analyzed by using a model of linear compression which assumes linear correlated energy chirp and linear dependence of a path length on energy deviation. Analysis of the density modulation growth due to coherent synchrotron radiation inside bends of the magnetic bunch compressor is done for the simplified case of no correlated energy chirp (no compression). Analytical results of this paper can be used for benchmarking numerical simulation codes.

Quantum coherence in nonlinear optical processes: theory and possible application to control of chemical reaction and quantum computation

Phase dependence in nonlinear optical processes reveals an intriguing interplay between the phase coherence of a short laser pulse and the laser-induced quantum wave-packet dynamics, which cannot be observed in the linear response regime. In this paper, the intra-pulse quantum coherence is demonstrated with three examples: molecular π pulses for total inversion of electron population, unexpected chirp dependence in multi-photon absorption yield, and active control of decoherence for quantum computation. These results demonstrate that quantum coherence is a unique method in the dynamic control of molecular systems, which cannot be achieved otherwise.

Chirp dependence in InGaAs/InAlAs multiple quantum well electro-absorptive modulators near polarization-independent conditions

We study the dependence of the chirp parameter on heavy- and light-hole energy splitting by analyzing the change in the absorption curve of different InGaAs/InAlAs p-i-n multiple quantum well structures designed for use in amplitude modulators. We observe, for the transverse electric mode, a high chirp parameter for the sample whose fundamental transition involves the light hole, whereas for samples whose fundamental transition involves the heavy hole, the more polarization sensitive the samples are, the smaller the chirp parameter is. This indicates that it is not possible to have tensile strained InGaAs/InAlAs multiple quantum well structures for electro-absorptive modulators which are simultaneously chirp-free and polarization independent.

Quantum Control of Population Transfer in Green Fluorescent Protein by Using Chirped Femtosecond Pulses

We demonstrate that the methods of quantum control can be applied successfully to very large molecules in room temperature liquid solution. Chirped femtosecond pulses are used to excite a green fluorescent protein mutant in both buffered aqueous solution and solid acrylamide gel. At high energy densities, the fluorescence shows a strong chirp dependence, with positively chirped pulses transferring almost 50% more population to the excited state than negatively chirped pulses. By measuring the photobleaching rate in the gel as a function of pulse chirp, we find that the data are consistent with the bleaching of the protein being due to a thermal mechanism rather than to an excited-state photoreaction.

Chirp-controlled ultrafast optical nonlinearities in semiconductors

We experimentally demonstrate that the differential transmission (DT) response of bulk semiconductors excited well above the band edge can be manipulated by chirping of the broadband excitation and readout pulses. In particular, the maximum transmission change in spectrally integrated DT experiments can be modified on the 20 fs time scale. Spectrally resolved DT studies explain this chirp dependence. Depending on the sign of the chirp, positive or negative DT contributions at low or high photon energies are probed with varying efficiency around zero time delay. These results demonstrate that chirp can become an additional degree of freedom for the optimization of device performance in ultrafast all-optical switching.

Intrapulse Dynamical Effects in Multiphoton Processes: Theoretical Analysis

Stationary and nonstationary multilevel models are formulated to analyze ultrafast multiphoton processes with emphasis on electronic and nuclear coherence of a near-resonant intermediate state. By identifying and characterizing three intrapulse dynamical mechanisms (sequential-resonance, chirp-following, and time-delay), a clear physical picture is developed for understanding the subtle chirp dependence in intrapulse pump−probe processes. The theoretical analysis in the paper provides not only a possible interpretation for a recent three-photon experiment but also a general theoretical framework for studying ultrafast multiphoton processes in atoms and molecules.

High-power femtosecond chirped pulse excitation of molecules in solution

The effects of varying the chirp and intensity of an ultrashort pulse exciting the molecules LD690 and LDS750 in room temperature liquid solutions are investigated experimentally and theoretically. For low-power excitation, we find that the absorption and amount of excited state population are independent of chirp, while for high-power excitation we observe a strong chirp dependence. The high-power data results from an intra-pulse pump-dump process which is enhanced by negatively chirped pulses and prevented by positively chirped pulses.

Chirp tailoring in Q-switched InGaAsP lasers usingelectroabsorption loss section

Chirp tailoring is demonstrated in Q-switched two-section InGaAsP lasers, with RF modulation applied to an electroabsorption section of high saturation intensity. The pulse time-bandwidth product is varied by a factor of /spl sim/4, by changing the DC bias of the gain section. Pulses which are almost transform-limited are obtained for the lowest biases. Gain-switching experiments performed with the same lasers only show a moderate chirp dependence with bias. The authors give theoretical background to interprete the different behaviours.