D. S. Citrin

Semiclassical theory of terahertz multiple-harmonic generation in semiconductor superlattices

A semiclassical theory is used to describe the emission of multiple electromagnetic harmonics in the terahertz (THz) regime due to coherent frequency-modulated Bloch oscillations in a superlattice driven by a strong THz field. A cutoff frequency to the harmonics linear in the applied THz field strength but independent of modulation frequency is predicted.

Picosecond dynamics of terahertz-sideband generation in far-infrared illuminated quantum wells

Optical excitation of a quantum well illuminated by a strong far-infrared (FIR) field is known to give rise to sidebands on the optical spectra separated from the fundamental by multiples of twice the FIR frequency Ω. In this study, we consider the picosecond dynamics of terahertz (THz) sideband formation using picosecond optical excitation pulses. We find that the emission at the THz sidebands largely tracks the temporal evolution of the excitation pulse. Applications to wavelength-division multiplexing are discussed.

Coherent control of quantum-well excitons in a resonant semiconductor microcavity for high-speed all-optical switching

Coherent control of excitons in quantum wells embedded in a resonant planar semiconductor microcavity versus in quantum wells without the cavity at high repetition rates is investigated theoretically to determine the practical constraints for application in high bit-rate optical switching. It is shown that /spl pi/-shifted pulse pairs are optimal to coherently populate and depopulate the QW on the 100-fs timescale. For the cavity-free case, the small optical nonlinearity will require devices incorporating /spl sim/100 quantum wells; the resonant enhancement of the confined mode for the case of the cavity leads to an effective increase in the optical nonlinearity and thus a reduction of the required number of quantum wells to /spl sim/10. In addition, switch architectures that avoid interferometers, and thus will have superior temperature and mechanical stability, based on the microcavity are proposed. We believe that although room-temperature operation of a 100-Gb/s switch based on this principle may be difficult, operation at liquid-nitrogen temperature should be feasible.

Constraints on coherent control of quantum-well excitons for high-speed all-optical switching

Coherent control of excitons in quantum wells at high repetition rates is investigated theoretically to determine the practical constraints for application in high-bit-rate optical switching. A tradeoff between optical pathlength (number of quantum wells) and excitation density is found that severely limits the applicability of this mechanism for implementation in 100-Gb/s optical systems.

Ultrafast modulation of semiconductor lasers through a terahertz field

We demonstrate, by means of numerical simulation, an interesting mechanism to modulate and switch semiconductor lasers at THz and sub-THz frequency rates. A sinusoidal terahertz field applied to a semiconductor laser heats the electron-hole plasma and consequently modifies the optical susceptibility. This allows an almost linear modulation of the output power of the semiconductor laser and leads to a faithful reproduction of the terahertz-field waveform in the emitted laser intensity.

Broadband terahertz emission through exciton trapping in a semiconductor quantum well.

Exciton trapping in a dc-biased quantum well is shown to result in the emission of broadband terahertz transients. The transients are free from bandwidth limitations, very intense, and quite distinctive.

Large-signal coherent control of normal modes in quantum-well semiconductor microcavity

We demonstrate coherent control of the cavity-polariton modes of a quantum-well semiconductor microcavity in a two-color scheme. The cavity enhancement of the excitonic nonlinearity gives rise to a large signal; modulating the relative phase of the excitation pulses between zero and π produces a differential reflectivity (ΔR/R) of up to 20%. The maximum nonlinear signal is obtained for cocircular pump and probe polarization. Excitation-induced dephasing is responsible for the incoherent nonlinear response, and limits the contrast ratio of the optical switching.

Interaction of terahertz transients and broadband optical pulses in quantum wells

A theoretical study of the interaction of intense terahertz transients and broadband optical pulses in quantum wells is presented. The approach is based on a numerical solution of the anisotropic semiconductor Bloch equations and includes, self-consistently, both continuum and excitonic effects. In the optical regime we recover the dynamic Franz–Keldysh effect showing THz sidebands in the optical absorption spectrum. In the THz regime we discern a series of harmonically generated upshifted THz transients. It is demonstrated pictorially that the upshifted transients are formed by the creation of highly anisotropic interfering, relative-motion electron–hole wave packets. We also investigate the influence of ellipticity of the driving field and chirped optical pulses. The field interaction with the quantum well is shown to be highly nonperturbative for typical free-electron laser fields. A series of propagating charge-carrier wave packets are analyzed, and a connection is made to analogies in the high-field physics of atomic ensembles.

Generation of 10-THz transients from a subpicosecond optical pulse and a 1-THz field in quantum wells

A quantum well simultaneously subjected to a 1 kV/cm, 1 THz field, and a 100 fs optical pulse is shown to result in emission of a sub-ps strong upshifted ∼10 THz transient.

Extraction of the frequency-domain optical response function of a periodically modulated medium with short optical pulses

The interaction of a short optical pulse with a medium whose optical properties are periodically modulated depends on the modulation phase at the moment of the pulse arrival. A technique of extracting the linear optical response function of such a medium to the cw optical field with a judiciously chosen series of short pulses rather than with cw optical fields is presented. An example of using the technique in numerical simulations is given, and a possible experimental arrangement is discussed. In particular, this technique may be convenient for extracting the optical properties of quantum wells modulated by a terahertz field.