High power femtosecond fiber laser systems typically rely on self-similar amplification, large scale chirped pulse amplification (CPA), or higher-order soliton pulse compression. In any of these system architectures the control or minimization of fiber nonlinearities is paramount. To date, the scalability of Er fiber lasers in particular has been limited due to their intrinsic anomalous dispersion (limiting self-similar amplification) and their small gain bandwidth (limiting CPA) whereas higher-order soliton compression generally limits pulse quality. Here, we address these limitations by enabling highly nonlinear pulse propagation in Er fiber amplifiers with minimal pulse distortions based on adaptive control of the input pulse. Though the system is subject to high levels of self-phase modulation, the output pulse quality remains high, moreover, the output bandwidth is greatly increased, easily surpassing the bandwidth limitation of classical CPA systems. Adaptive control is enabled via a compact adaptive chirped fiber Bragg grating (FBG) pulse shaper/stretcher, paired with a matched, static FBG compressor. We generate 110 nJ pulses, with a FWHM of 62 fs in a single mode Er fiber amplification system at a repetition rate of 99.8 MHz, corresponding to an average power of 11.0 W. This corresponds to a maximum peak power of 1.4 MW, which should yield focused intensities above 1 TW/cm2, providing the high intensity and repetition rate needed to combine strong-field effects such as high harmonic generation in solids with the precision of frequency combs. At a lower 25 MHz repetition rate, we reach 340 nJ, 63 fs.
Experiments done with single photons in the early 1990's produced a surprising result: that single photons pass through
a photonic tunnel barrier with a group velocity faster than the vacuum speed of light. This result has stimulated intense
discussions related to causality, the speed of information transfer, the nature of barrier tunneling and the meaning of
group velocity. The superluminality of tunneling photons is now textbook material, although the authors note that
controversy still remains. Another paradoxical result, known as the Hartman effect, is that the tunneling time of the
photons becomes independent of barrier length in the limit of opaque barriers. In this paper we examine the meaning of
group velocity in the context of barrier tunneling. We ask whether a single tunneling photon can be described by a
group velocity and whether the short group delays imply superluminal group velocity. We resolve the paradox of the
Hartman effect and show that the predicted and measured group delays are not transit times but photon lifetimes.
Interelement optical coupling introduces microwave frequency time constants to semiconductor laser array systems. The phenomenon is related to beating between lateral array modes and can take place at frequencies from 10 to 50 GHz for typical array designs employing index guided elements. Linearized coupled rate equation analysis has previously found small-signal modulation resonances at those frequencies. Here, the full rate equation theory is used for large signal analysis and novel schemes for utilizing those microwave frequency resonances for high speed optical signal transmission are theoretically demonstrated. We show, for example, that digital signals with bit rates many times the relaxation oscillation frequency are possible in principle.
In this paper we consider the spontaneous emergence of organized behavior and spatio-temporal
chaos in an array of coupled semiconductor lasers. In the absence of coupling, each laser in the array
exhibits a constant, steady state output intensity in response to a constant input pump current. For constant
pump currents above lasing threshold, the individual lasers do not exhibit any interesting instabilities such as
chaos. In the presence of coupling, the constant steady state can lose its stability and non-trivial
spatio-temporal complexity results. The nature of the spatio-temporal dynamics depends on the strength of
the coupling between adjacent elements. For low coupling strengths the stable steady state is one in which
the fields in adjacent elements have nearly equal amplitudes and a phase difference close to 'ii. As the
coupling is increased a Hopf bifurcation to a spatially ordered and temporally periodic output is obtained.
Further increases in coupling strength lead to full blown spatio-temporal chaos.
Conference Committee Involvement (3)
The Nature of Light: What are Photons? IV
22 August 2011 | San Diego, California, United States
The Nature of Light: What are Photons? III
3 August 2009 | San Diego, California, United States
The Nature of Light: What are photons?
26 August 2007 | San Diego, California, United States
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