Generation of mid-IR radiation in near-IR semiconductor lasers based on low-dimensional heterostructures

A method for generating mid-IR radiation (λ ～ 10μm) in near-IR (λ ～1 μm) quantum-well semiconductor heterolasers has been proposed. This method is based on the formation of population inversion at a mid-IR intersubband transition as a result of the depletion of its lower level by a strong near-IR field. In contrast to the previous investigations of this problem, the inhomogeneous broadening of the noted transition (caused by the dependence of its frequency on the carrier energy) is taken into account, and it is proposed to invert it not in the entire spectral range but only in the region resonant with the mid-IR field. This approach makes it possible to significantly reduce (in comparison with the previous estimates) the threshold pump current density for initiating mid-IR generation and, as a result, hope to implement operation of the proposed laser at room temperature in the cw mode.     

Nonlinear circuit model for semiconductor lasers

The multimode rate equations are transformed to the circuit equations of the electro-optical system by expressing the charge carrier concentrations and recombination rates in terms of voltage across the active layer, and representing the photon densities of the respective modes by a set of voltages. By proper approximation of functions describing the recombination rates, the equivalent circuit can be composed of conventional linear and nonlinear circuit components.     

Electromagnetic radiation control in metallic waveguide with gyrotropic semiconductor wall

New possibilities of using magnetoplasma effects in semiconductors for the millimeter radiation control are discussed. For this purpose a highly-conductive semiconductor plate has been substituted for a part of the wide wall of metallic rectangular waveguide and the external magnetic field has been directed perpendicularly to the plate surface. It is shown that this construction can be used both as a second — harmonics filter and a directional coupler.     

Generation of Terahertz radiation with two color semiconductor lasers

We discuss and analyze concepts for the generation of tuneable continuous wave terahertz (THz) radiation with two color diode lasers. First, different geometries of two color lasers are reviewed. We show that the THz power of two color lasers in combination with external photomixers becomes sufficient for scanning THz imaging applications when optical amplification with a tapered amplifier is implemented. Then, the concept of direct emission of THz radiation out of a two‐color semiconductor laser is reviewed and the potential of this concept with respect to THz bandwidth and achievable THz power is critically analyzed.     

周期变截面波导中的多缺陷态*

设计了一种具有对称结构的多缺陷周期变截面波导,并在其Bragg禁带中实现了多缺陷态的产生。研究表明,通过调整缺陷的个数和长度可实现对缺陷态数目的选择和缺陷态中心频率的调谐。另外,改变重复周期个数可对缺陷态的带宽进行调节。通过对各缺陷态的声场分布进一步分析,我们发现声压沿波导中心轴呈对称或反对称分布。对称缺陷态的最大声能量总是向长度较小的缺陷处偏移,而反对称缺陷态则相反,总是向长度较大的缺陷处偏移。利用这种偏移特性可实现对多缺陷态的声场调控。这不仅使我们对声缺陷态的认识更加深入,更有利于功能型声波导器件的发展与应用。     

Nonlinear dynamics of doped semiconductor quantum dot lasers

We discuss the influence of wetting layer doping on the turn-on dynamics of a quantum dot (QD) laser by using a microscopically based rate equation model which separately treats the dynamics of electrons and holes. As the carrier-carrier scattering rates depend nonlinearly on the wetting layer carrier densities we observe drastic changes of relaxation oscillation frequency and damping if the wetting layer is doped. We gain insight into the nonlinear dynamics of the QD laser by a detailed analysis of various sections of the five-dimensional phase space focusing on changes in the coupling between QD electron and holes dynamics.     

Astigmatism of the radiation of semiconductor stripe-geometry lasers

The effect of injection current on the intensity and angular distribution of radiation in TE- and TM-polarized modes of diode lasers with a stripe geometry and double GaAs-AlGaAs-based heterostructure is investigated. The analysis of the angular distribution of radiation revealed the nonmonotonic behavior of its astigmatism with increase in the current. The coefficient of astigmatism in the mode of lasing is substantially higher for the TE-mode than for the TM-mode. An increase in radiation astigmatism is accompanied by a decrease in the differential effectiveness and polarization degree. These specific features are explained by the interaction of the defocusing action of distribution of the refractive index n(x) in the plane of the p-n-transition with a minimum under the center of the stripe contract (at x=0) with the focusing action of the gain coefficient distribution. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 461–464, July–August, 2000.     

810-nm InGaAlAs/AlGaAs double quantum well semiconductor lasers with asymmetric waveguide structures

The 810-nm InGaAlAs/AlGaAs double quantum well （QW） semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conver- sion efficiency at continuous-wave （CW） power output. The threshold current density and slope efficiency of the device are 180 A/cm^2 and 1.3 W/A, respectively. The internal loss and the internal quantum efficiency are 1.7 cm^-1 and 93%, respectively. The 70% maximum power conversion efficiency is achieved with narrow far-field patterns.     

Nonlinear semiconductor lasers and amplifiers for all-optical information processing

The nonlinear properties of semiconductor lasers and laser amplifiers when subject to optical injection are reviewed and new results are presented for multisection lasers, vertical cavity semiconductor optical amplifiers, and surface-emitting lasers. The main underlying material parameters are outlined and the key design approaches are discussed for both edge-emitting and vertical cavity devices. An overview of theoretical modeling approaches is discussed and a summary of key experimental results is presented. The practical use of optically injected edge-emitting and vertical cavity semiconductor lasers and laser amplifiers is illustrated with examples of applications including, among others, optical logic and chaotic communication.     

Analytical model of a corrugated optical waveguide

An analytical model of the diffraction energy exchange between the radiative and the waveguide modes in a planar optical waveguide corrugated by a waveguide grating with an arbitrary form of teeth is developed on the basis of the coupled-wave method. It is shown that the mechanism of the energy exchange between the modes is determined by the partial interaction of all components of the spatial frequency spectrum of the waveguide modes with the corresponding components of the spatial frequency spectrum of the grating. It is established that gratings with an asymmetric tooth profile providing a shift of the peak of the spatial frequency spectrum toward matching are characterized by a higher diffraction efficiency α; however, at small thicknesses δ of the waveguide grating, the efficiency is almost independent of the tooth profile. It is shown that gratings with a symmetric profile give on average a decreasing dependence α(δ), while gratings with an optimized asymmetric profile yield a monotonically increasing saturating dependence α(δ).     

Directionality and mode structure of radiation of semiconductor lasers with electron-beam pumping

We present results of investigations of the directionality diagram and mode structure of radiation of semiconductor lasers with electron pumping that have microrelief reflectors instead of a blind mirror and output mirrors, whose coefficient of reflection depends on the wavelength and the angle of light propagation. Application of such mirrors allows one to narrow the spectrum of output radiation of the lasers, simultaneously reducing the threshold and increasing the output power. The discovered multilobe structure of the directionality diagrams is explained on the basis of geometrical optics. The possibility of controlling the directionality of radiation depending on the spectral and angular characteristics of the output mirror is shown. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 092–697, Septemter–October, 1999.     

Transverse mode competition in defect states of a waveguide with corrugated walls

We investigate the defect states arising in the Bragg and non-Bragg gaps by inserting a straight duct into a waveguide with periodically corrugated walls. In periodic waveguides, the Bragg gap is created by the interference of the same transverse modes whereas the different mode coupling leads to the non-Bragg one. Due to the involved high-order modes, there are two defect states observed in the non-Bragg gap while only one in the Bragg gap, indicating that transverse modes play a significant role in the creation of defect states. Furthermore, the frequency of each defect state highly relies on the defect geometries and their band widths can be optimized by the number of waveguide segments. The proposed transverse mode competition analysis reveals the mechanism of frequency shifting and provides an opportunity for guided wave control engineering, which would definitely benefit their applications in various functional devices, such as filters, sensors, and amplifiers.     

Direct acceleration of electrons in a corrugated plasma waveguide

Historically, direct acceleration of charged particles by electromagnetic fields has been limited by diffraction, phase matching, and material damage thresholds. A recently developed plasma micro-optic [B. Layer, Phys. Rev. Lett. 99, 035001 (2007)] removes these limitations and promises to allow high-field acceleration of electrons over many centimeters using relatively small femtosecond lasers. We present simulations that show a laser pulse power of 1.9 TW should allow an acceleration gradient larger than 80 MV/cm. A modest power of only 30 GW would still allow acceleration gradients in excess of 10 MV/cm.     

High quality resonances for terahertz radiation diffraction at periodically corrugated semiconductor interfaces

It is shown that the resonance features analogous to the well known optic Wood-type anomalies can be observed in the THz region for diffraction at periodically profiled semiconductor surfaces. The analytical theory of such resonance processes caused by excitation of surface plasmon polaritons (SPPs) is developed. It is shown that strong resonance effects such as total suppression of the specular reflection (TSSR) can be achieved for rather small inclinations of harmonic gratings. The analytical theory predictions are confirmed by strict numerical simulations. The analytical approach presented allows one to find parameters of the gratings so that the resonance diffraction results in specific redistributions of the reflected energy between different diffraction channels. As an example we demonstrate parameters of the InSb biharmonic grating responsible for the TSSR accompanied by 50% reflection in the minus first diffraction order when the SPP is excited in the plus first diffraction order.     

High-gain wide-band gyrotron traveling wave amplifier with a helically corrugated waveguide

First bandwidth measurements of a novel gyrotron amplifier are presented. The coupling between the second harmonic cyclotron mode of a gyrating electron beam and the radiation field occurred in the region of near infinite phase velocity over a broad bandwidth by using a cylindrical waveguide with a helical corrugation on its internal surface. With a beam energy of 185 keV, the amplifier achieved a maximum output power of 1.1 MW, saturated gain of 37 dB, linear gain of 47 dB, saturated bandwidth of 8.4 to 10.4 GHz ( 21% relative bandwidth), and an efficiency of 29%, in good agreement with theory.     

Dynamics of beams in a periodically corrugated plasma-filled waveguide with a polynomial corrugation profile

The problem of beam dynamics in a periodically corrugated plane waveguide filled partially with nonmagnetized plasma is considered. Short-period beam trajectories of purely waveguide type and plasma-waveguide types are found. The distribution function of beam reflection points from the waveguide surface in the case of chaotic trajectories is calculated. Radiophysical Nuclear Research Center, All-Russia Institute of Electronic Physics, Sarov, Nizhny Novgorod region, Russia Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 479–490, April, 1997.     

Optimization of frequency-modulated pulse compression in a sectioned waveguide with a helically corrugated surface

A method of considerably elevating (by 20–30 times) the peak power of frequency-modulated microwave pulses by passive compression in a waveguide with a helically corrugated surface used as a dispersive medium is considered. It is shown that the use of a sectioned compression waveguide (i.e., a waveguide consisting of several sections connected to each other with slightly differing parameters) considerably improves precise tuning of the dispersion characteristic of the system to a desired law of frequency modulation of an input pulse. An algorithm for selecting optimal parameters of the sections is developed, and a high efficiency of the method is demonstrated by several examples.     

Electromagnetic wave radiation through the gyrotropic semiconductor wall of rectangular waveguide

The peculiarities of the microwave radiation through the semiconductor wall of the rectangular metallic waveguide set in the external magnetic field have been investigated. The radiation direction dependence on wave frequency, the external magnetic field, and the geometric shape of the semiconductor element have been determined. It has been shown that in the case of the wedge-like semiconductor element the radiation direction can be controlled by the external magnetic field. The experiments have been carried out in V-band at the temperature of liquid nitrogen.