Igor A. Sukhoivanov

Photonic crystals : physics and practical modeling

to Photonic Crystals.- Fundamentals of Wave Optics.- Fundamentals of Computation of Photonic Crystal Characteristics.- Band Structure Computation of 1D Photonic Crystals.- Band Structure Computation of 2D and 3D Photonic Crystals.- Finite-Difference Time-Domain Method for PhC Devices Modeling.- Photonic Crystal Optical Fibers.- FDTD Method for Band Structure Computation.- Photonic Crystal Waveguides.- Application for Design and Simulation of Optical WDM Demultiplexer.

Femtosecond parabolic pulse shaping in normally dispersive optical fibers.

Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initial pulse duration, chirp and energy. Applicability of different fibers for femtosecond pulse shaping is analyzed. Recommendation for shortest parabolic pulse formation is made based on the analysis presented.

Ultrafast gain dynamics in asymmetrical multiple quantum-well semiconductor optical amplifiers

A numerical model for the investigation of the ultrafast gain properties in asymmetrical multiple quantum-well semiconductor optical amplifiers has been developed considering propagation of ultrashort optical pulses with different wavelengths. The dynamics of the number of carriers and carrier temperature are investigated for each quantum well. The results agree with the experimental results of pump probe measurements with different wavelengths. It is shown that gain recovery is slower for higher energy wells for pump signals of all wavelengths.

Supercontinuum generation at 800 nm in all-normal dispersion photonic crystal fiber

We have numerically investigated the supercontinuum generation and pulse compression in a specially designed all-normal dispersion photonic crystal fiber with a flat-top dispersion curve, pumped by typical pulses from state of the art Ti:Sapphire lasers at 800 nm. The optimal combination of pump pulse parameters for a given fiber was found, which provides a wide octave-spanning spectrum with superb spectral flatness (a drop in spectral intensity of ~1.7 dB). With regard to the pulse compression for these spectra, multiple-cycle pulses (~8 fs) can be obtained with the use of a simple quadratic compressor and nearly single-cycle pulses (3.3 fs) can be obtained with the application of full phase compensation. The impact of pump pulse wavelength-shifting relative to the top of the dispersion curve on the generated SC and pulse compression was also investigated. The optimal pump pulse wavelength range was found to be 750 nm < λp < 850 nm, where the distortions of pulse shape are quite small (< -3.3 dB). The influences of realistic fiber fabrication errors on the SC generation and pulse compression were investigated systematically. We propose that the spectral shape distortions generated by fiber fabrication errors can be significantly attenuated by properly manipulating the pump.

Electrical reorientation of liquid crystal molecules inside cylindrical pores for photonic device applications

We present the simulated distribution of the local director of a nematic liquid crystal inside cylindrical macropores under the influence of an electric field. The Frank free energy approach is used to describe the nematic behavior. The influence of both molecular anchoring strength and pore radius is investigated. The results of this analysis are applied for simulation of an electrically tunable microcavity based on porous silicon infiltrated with a liquid crystal. The Bruggeman approximation is used while calculating the effective refractive index of each layer in the porous silicon multilayer structure. The reflectivity spectrum of the latter is simulated using the transfer matrix approach. The electrical tuning range of a microcavity designed for near-infrared waves is found to vary from 10.5 up to 23 nm for weak and strong surface anchoring conditions, respectively.

Formation of ultrashort triangular pulses in optical fibers

Specialty shape ultrashort optical pulses, and triangular pulses in particular, are of great interest in optical signal processing. Compact fiber-based techniques for producing the special pulse waveforms from Gaussian or secant pulses delivered by modern ultrafast lasers are in demand in telecommunications. Using the nonlinear Schrödinger equation in an extended form the transformation of ultrashort pulses in a fiber towards triangular shape is characterized by the misfit parameter under variety of incident pulse shapes, energies, and chirps. It is shown that short (1-2 m) conventional single mode fiber can be used for triangular pulse formation in the steady-state regime without any pre-chirping if femtosecond pulses are used for pumping. The pulses obtained are stable and demonstrate linear chirp. The ranges and combinations of the pulse parameters found here will serve as a guide for scheduling the experiments and implementation of various all-fiber schemes for optical signal processing.

Improvement of characterization accuracy of the nonlinear photonic crystals using finite elements-iterative method

We investigate nonlinear one- and two-dimensional photonic crystals by applying a finite element-iterative method. Numerical results show the essential influence of nonlinear elements embedded into a quarter-wave stack and the sharp photonic crystal waveguide bend on the spectral characteristics of these structures. We compare our results with those obtained in [21] from the discrete equation method for the case of a sharp waveguide bend. The comparison shows that neglecting the nonuniform field distribution inside the embedded nonlinear elements leads to overestimation of the waveguide bend transmissivity.

How to restrain Auger recombination predominance in the threshold of asymmetric bi-quantum-well lasers

Both radiative and nonradiative processes which occur in the active region of GaInAs–GaInAsP–InP asymmetric multiple quantum-well (AMQW) heterolasers with two quantum wells of different width (4 and 9 nm) are described. Several possible processes of non-radiative Auger recombination which affect the temperature sensitivity of the lasing threshold are analyzed and the temperature dependencies of the investigated processes are presented. For the above-mentioned AMQW heterostructure, it is shown that the influence of the Auger recombination processes on the temperature behaviour of the lasing threshold can be restrained by operation at temperatures lower than 340 K and the cavity losses which do not exceed 60 cm K1 .

Theoretical Study of Optical Transition Matrix Elements in InGaN/GaN SQW Subject to Indium Surface Segregation

We investigate the dependence of dipole matrix elements for InGaN/GaN single quantum well structures on the indium surface segregation (ISS). Obtained results show that the influence of the surface segregation on the dipole matrix element is not equal for all optical transition. This effect results from the joint action of the piezoelectric polarization and ISS that change selection rules. In addition, surface segregation at each interface of the quantum well has different impact on optical characteristics depending on the direction of the piezoelectric polarization. The effect of the surface segregation has been estimated applying the global sensitivity analysis in the frame of six-band approximation for the valence band and parabolic approximation for the conduction band.

Chirp compression with single chirped mirrors and its assembly

Chirped mirrors are widely used in ultrafast optics as broadband devices for dispersion compensation. Time domain analysis in contrast to frequency domain one allows the direct investigation of pulse profile changing during chirp compression. We model the chirped pulse compression with single chirped mirror and assembly of similar mirrors. Our analysis shows there is similar effect of chirp compensation in both cases. However, injurious group delay oscillations in the single mirror strongly decrease pulse quality in assembly of mirrors and can even damage pulse waveform. Angle of incidence and polarization also play crucial role and should be taken into account.