Gennady A. Smolyakov

Surface plasmon modes of finite, planar, metal-insulator-metal plasmonic waveguides

The numerical analysis of finite planar metal-insulator-metal waveguide structures using the transfer-matrix formalism reveals both bound and leaky surface plasmon (SP) modes. The dispersion relations, propagation lengths and confinement factors of these SP modes are presented. The highest energy SP mode consists of non-radiative (bound) and radiative (leaky) portions separated by a spectral gap. The leaky regime is further divided into antenna and reactive mode regions. The antenna mode may be used for both free-space coupling and beam steering devices.

Large S-section-ring-cavity diode lasers: directional switching, electrical diagnostics, and mode beating spectra

Semiconductor lasers with monolithically integrated ring cavities exceeding 1 cm in perimeter were fabricated and characterized optically and electrically. Directional switching was observed, influenced by S-section seeding of unidirectional operation. The lasing threshold was identified by differential current-voltage measurements, which are also shown to be useful in monitoring directional switching. Mode beating was observed at three radio-frequency bands: 7.6, 15.2, and 22.9 GHz.

Frequency beating between monolithically integrated semiconductor ring lasers

Optoelectronic integrated circuits incorporating a pair of optically independent large-cavity semiconductor ring lasers (SRLs), directional couplers, waveguides, Y-junction mixer, and photodetectors are demonstrated. Counterclockwise and clockwise output beams from the two SRLs are collected separately and mixed prior to detection. Frequency beating between modes of two SRLs is measured. The beat frequency is fine-tuned by an integrated Joule heater, designed for thermal control of the lasing wavelength. No signs of frequency lock-in in the vicinity of zero detuning are observed, which makes this structure a promising candidate for applications in ring laser gyros and optical rotation sensors.

Highly unidirectional InAs∕InGaAs∕GaAs quantum-dot ring lasers

We report fabrication and characterization of semiconductor ring lasers with quantum-dot active region. The InAs∕InGaAs∕GaAs “dots-in-a-well” ridge-waveguide ring lasers are monolithically integrated with coupling waveguides and monitoring quantum-dot photodetectors. The lowest threshold current density for semiconductor ring lasers is demonstrated. When enhanced by a forward biased S-section waveguide, stable unidirectional operation with record suppression ratio of counterpropagating waves exceeding 30dB is achieved.

Rapid degradation of CdSe/ZnS colloidal quantum dots exposed to gamma irradiation

Effects of Cs137 gamma irradiation on photoluminescent properties of CdSe∕ZnS colloidal quantum dots are reported. Optical degradation is evaluated by tracking the dependence of photoluminescence intensity on irradiation dose. CdSe∕ZnS quantum dots show poor radiation hardness, and severely degrade after less than 20kR exposure to 662keV gamma photons.

Temperature and thickness dependence of steam oxidation of AlAs in cylindrical mesa structures

The Deal-Grove model of thermal oxidation kinetics is adapted to cylindrically symmetric mesa structures and applied to study steam oxidation of AlAs. Oxidation process parameters are extracted from available experimental data as functions of temperature and the AlAs layer thickness. The oxidation rate is found to be very sensitive not only to temperature, but also to the oxidation front position inside the mesa. The oxidation rate slows down as the oxidation front moves into the mesa, reaches a minimum, and then accelerates at the final stages of the oxidation process. Complex nonmonotonic dependence of the oxidation process on layer thickness is also revealed.

Self-consistent calculation of current self-distribution effect in GaAs-AlGaAs oxide-confined VCSELs

A three-dimensional electrical-thermal-optical numerical solver is applied to model GaAs-AlGaAs-based top-emitting oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with GaAs multiple-quantum-well active region. Continuous-wave mode of operation is simulated over a range of voltages, covering the subthreshold spontaneous emission and lasing emission. The effect of self-distribution of electrical current is demonstrated for the first time in self-consistent electrical-thermal-optical simulation of VCSELs.

Iron Oxide Nanocrystals for Magnetic Hyperthermia Applications

Magnetic nanocrystals have been investigated extensively in the past several years for several potential applications, such as information technology, MRI contrast agents, and for drug conjugation and delivery. A specific property of interest in biomedicine is magnetic hyperthermia—an increase in temperature resulting from the thermal energy released by magnetic nanocrystals in an external alternating magnetic field. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field strengths of 9 and 25 mT. Polymorphous nanocrystals as well as spherical nanocrystals and nanowires in paramagnetic to ferromagnetic size range exhibited good heating power. A remarkable 30 °C temperature increase was observed in a nanowire sample at 111 kHz and magnetic field of 25 mT (19.6 kA/m), which is very close to the typical values of 100 kHz and 20 mT used in medical treatments.

High-Speed Modulation Analysis of Strongly Injection-Locked Semiconductor Ring Lasers

A novel scheme for modulation bandwidth enhancement is presented, involving distributed Bragg reflector master laser monolithically integrated with strongly injection-locked whistle-geometry microring laser. Enhanced high-speed performance of the novel scheme is confirmed through numerical modeling by comparing it with an earlier scheme, where optical injection was provided by a waveguide directional coupler adjacent to the ring laser.

Synthesis and characterization of core/shell Fe3O4/ZnSe fluorescent magnetic nanoparticles

We report on the successful preparation and characterization of fluorescent magnetic core∕shell Fe(3)O(4)∕ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core∕3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission∕excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core∕shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe(3)O(4)) and nonmagnetic (ZnSe) phases. Compared to a reference Fe(3)O(4) NP sample, the room-temperature Néel relaxation time in core∕shell NPs is three times longer.