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We propose an electrically pumped intersubband laser capable of operating at short infrared wavelengths ∼1.5–2.5 μm. Short-wavelength operation is achieved via resonant intracavity second harmonic generation in quantum cascade (QC) lasers based on high band offset heterostructures. This approach overcomes the fundamental problem of intervalley scattering that prohibits direct lasing in QC lasers in this spectral range. The proposed devices can be modulated at a rate exceeding 100 GHz, which may be interesting for a variety of applications. We present detailed calculations of bandstructure design, phase-matched waveguide, and current-output power dependence for the devices based on GaInAs/AlAsSb/InP heterostructures. Accurate position of highly excited subbands is determined by calculating the conduction band (CB) dispersion with the energy-dependent 14-band effective mass, in which matrix elements are adjusted to fit the CB structure obtained with a 30-band k·p method. We also discuss the controversial location of lateral valleys, which imposes the limitation on the fundamental laser transition energy. [ABSTRACT FROM AUTHOR]

We calculate the nonlinear optical response of graphene in strong magnetic and optical fields, using a quantum-mechanical density-matrix formalism. We show that graphene in a magnetic field possesses a giant mid- or far-infrared optical nonlinearity, perhaps the highest among known materials. The high nonlinearity originates from unique electronic properties and selection rules near the Dirac point. As a result, even one monolayer of graphene gives rise to an appreciable nonlinear frequency conversion efficiency for incident infrared radiation. [ABSTRACT FROM AUTHOR]

We overview the results of recent experimental and theoretical studies of nonlinear dynamics of mid-infrared quantum cascade lasers (QCLs) associated with nonlinear interactions of laser modes. Particular attention is paid to phase-sensitive nonlinear mode mixing which turns out to be quite prominent in QCLs of different kinds and which gives rise to frequency and phase locking of laser modes. Nonlinear phase coupling of laser modes in QCLs leads to a variety of ultrafast and coherent phenomena: synchronization of transverse modes, beam steering, the RNGH multimode instability, and generation of mode-locked ultrashort pulses. [ABSTRACT FROM AUTHOR]

We analyze the dynamics of broad-area mid-infrared quantum cascade lasers (QCLs). We show the possibility of the coherent coupling of several transverse modes which results in several interesting effects including frequency and phase locking between transverse modes, bistability, and beam steering. We present an analytical model for the modal dynamics and its numerical analysis. Effects of amplitude and phase fluctuations on the modal stability are explored. We compare our theoretical results with our experimental measurements of buried heterostructure QCLs. [ABSTRACT FROM AUTHOR]

We demonstrate a quasiphase matching scheme for second-harmonic generation in quantum cascade lasers with integrated resonant nonlinearity. Modulation of the nonlinear susceptibility is achieved by the periodic modulation of the bias voltage along the ridge waveguide leading to a periodic shift of electronic resonances and a change in the electron population in different energy levels. An up to tenfold enhancement of the conversion efficiency is observed. This technique is applicable to any resonant nonlinear optical process in quantum wells. [ABSTRACT FROM AUTHOR]

About a 100-fold improvement of the second-harmonic generation in a quantum-cascade laser with integrated optical nonlinearity was obtained by including phase-matching considerations in the design of the deep-etched ridge waveguide. The waveguide layer structure was optimized to minimize the phase mismatch of the zero-order mode of the fundamental light with the second-order transverse mode of the second-harmonic light. Exact phase matching is made possible by the faster decrease of the modal refractive index of the fundamental light with decreasing ridge width relative to the refractive index of the second-harmonic light. Up to 240 μW of the second-harmonic power and a nonlinear power conversion efficiency of up to 36 mW/W2 were achieved. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Entangled photon states attract tremendous interest as the most vivid manifestation of nonlocality of quantum mechanics and also for emerging applications in quantum information. Here we propose a mechanism of generation of polarization-entangled photons, which is based on the nonlinear optical interaction (four-wave mixing) in graphene placed in a magnetic field. Unique properties of quantized electron states in a magnetized graphene and optical selection rules near the Dirac point give rise to a giant optical nonlinearity and a high rate of photon production in the mid- or far-infrared range. A similar mechanism of photon entanglement may exist in topological insulators where the surface states have a Dirac-cone dispersion and demonstrate similar properties of magneto-optical absorption. [ABSTRACT FROM AUTHOR]