We have investigated ultrashort parabolic pulse formation via passive nonlinear reshaping in normal dispersive optical fibers at 1550 nm. It was investigated parabolic pulse formation in the transient-state regime and in the steady-state regime. Numerical simulations have been made based on generalized nonlinear Schrödinger equation taking into account high-order dispersion terms and high order nonlinear terms. It was examined the applicability of different commercially available fibers for parabolic pulse formation at 1550 nm. It was found that small amount of positive second-order dispersion and quite sufficient third-order dispersion can restrict strongly the formation of parabolic pulses at 1550 nm. The most suitable fiber for pulse reshaping has been found.
Microstructured fibers have recently become popular due to their numerous applications for fiber lasers,1 super-continuum generationi2 and pulse reshaping.3 One of the most important properties of such fibers that is taken into account is its dispersion. Fine tuning of the dispersion (i.e. dispersion management) is one of the crucial peculiarities of the photonic crystal fibers (PCFs)4 that are particular case of the microstructured fibers.
During last years, there have been presented various designs of the PCFs possessing specially-designed dispersion shapes. 5-7 However, no universal technique exists which would allow tuning the PCF dispersion without using optimization methods.
In our work, we investigate the sensitivity of the PCF dispersion as respect to variation of its basic parameters. This knowledge allows fine-tuning the position of local maximum of the PCF dispersion while maintaining other properties unchanged.
The work is organized as follows. In the first section we discuss the dispersion computation method that is suitable for the global sensitivity analysis. The second section presents the global sensitivity analysis for this specific case. We also discuss there possible selection of the variable parameters.
We present an analysis of the guided modes of a one-dimensional photonic bandgap waveguide which consists of a low refractive index guiding layer sandwiched between two Bragg mirrors. The layers in the mirrors are aperiodically arranged according to the Kolakoski K(1; 2) substitutional rules and their parameters are chosen in such a way that the omnidirectional reflection is achieved. Using the transfer matrix formalism, both the bandgap conditions and dispersion characteristics of the guided modes of such OmniGuide structure are studied.
Here we propose a simple design for a solid-core photonic crystal fiber made of silica by keeping the golden ratio
(1.618) between pitch and air hole diameter Λ /d in a subset of six rings of air-holes with hexagonal arrangement. In the
case when we have a pitch equal to one micron (Λ =1 μm), we need air-holes diameters d=0.618 μm in order to obtain
the golden ratio parameter (Λ/d=1.618), and achieve two zero dispersion wavelength (ZDW) points at 725 nm and 1055
nm; this gives us the possibility to use this fiber in supercontinuum generation using a laser emission close to that points.
We analyzed a series of fibers using this relation and show the possibilities of tunable ZDW in a wide range of
wavelengths from 725 nm to 2000 nm with low losses and small effective area. In agreement with the ZDW point
needed, the geometry of the structure can be modified to the point of having only three rings of air holes that surround
the solid core with low losses and good confinement mode. The design proposed here is analyzed using the finite
element method (FEM) with perfectly matched layers (PML), including the material dispersion directly into the model
applying the Sellmeier’s equation.
The supercontinuum (SC) generated by pumping in anomalous dispersion is sensitive to the input pulse fluctuations and pump laser’s shot noises and does not possess a single-pulse waveform, so the incident pulse becomes a noise-like train of spikes. A simple method of creating pulsed lasers with either pulse-maintaining ultrabroad SC or specially shaped pulse waveforms can be implemented using all-normal-dispersion microstructured optical fibers (ANDi-MOFs). An ANDi-MOF with a simple topology and dispersion profile maximum at 800 nm was designed using the effective index method. Its properties and suitability were characterized via numerical simulation of femtosecond parabolic pulse formation and generation of an octave-spanning pulse-maintaining SC using a generalized propagation equation. The designed ANDi-MOF is suitable for resolving both problems and allows some detuning of the pulse’s wavelength around 800 nm. However, a better choice for SC generation is pumping at or near the wavelength where the third-order dispersion becomes zero. This configuration benefits from the absence of pulse break-up under large pulse energies, which appears otherwise. The fiber can provide a low-cost method for developing supercontinuum sources and a solution to the problems of parabolic waveform formation to meet the needs of optical signal processing and pulse amplification and compression.
In the work, we have presented the technique based on the graphics processing unit accelerated finite-difference time-domain (FDTD) method for characterization of a single-mode photonic crystal fiber (PCF) with an arbitrary refractive index profile. In contrast to other numerical methods, the FDTD allows studying the mode propagation along the fiber. Particularly, we have focused attention on the method details that allowed us to reduce dramatically the computation time. It has been demonstrated that the accuracy of dispersion obtained by the FDTD method is comparable to the one provided by the finite elements method while possessing lower computation time. The method has been used to determine the fundamental mode cut-off of all-normal dispersion PCF and to find fiber losses beyond this wavelength.
In the work, we have presented the technique based on the FDTD method for the dispersion computation of a single-mode ber with an arbitrary refractive index pro le. In contrast to other numerical methods the FDTD allows studying the beam propagation along the ber taking into account material dispersion and the nonlinearity. Particularly, we have concentrated attention on the method details that allowed us to reduce dramatically the computation time and achieve the accuracy close to the one provided by the nite elements method.
We have designed an all-normal dispersion photonic crystal fiber optimized for pumping at 800 nm with initial pulses which are typical for conventional Ti:Sapphire lasers. Parabolic pulse formation and supercontinuum generation in this fiber is analyzed both in time and frequency domains.
Photonic crystal (PhC) waveguides are the prospective structures for high-speed optical micro-devices. Possessing high-effective light localization, such waveguides allow introducing active materials making additional all-optical signal control possible. The most effective from the technological point of view is embedding the PhC filters with characteristics close to the ones of the background PhC (i.e. with the same refractive index, PhC period, etc.). As has been shown in previous papers,1, 2 such filters possess spectral characteristics that allow using them for processing the ultra-short pulses in case of either passive (implemented with linear materials) of active (with nonlinear materials) devices. Moreover, from the technological point of view such PhC waveguides with filters can be easily integrated into the electronic circuit which reduces costs and production time.
Unfortunately, optical losses and back reflection from such a filters makes them unsuitable for high-speed integrated optical circuits.
In this work we propose analysing both density of modes (DOM) and the transmission spectra to optimize the parameters of the PhC filters made of linear or nonlinear material.
Proposed characteristics have been first introduced to optimize the PhC filters used for wavelength division demultiplexing.3 However, since waveguiding properties have not been taken into account, the photonic density of states maps as well as transmittance maps can be applied with high accuracy to a bulk PhC but not to confined PhC filter. Taking into account waveguiding properties provides great enhancement to the precision of characterization of the confined PhC filters.
The one-dimensional aperiodic structure is considered which is formed by stacking together chiral and achiral
layers according to the Kolakoski self-generation scheme. Numerical simulations are carried out for different
structure configurations to reveal the dependence of the optical characteristics of the system on the generation
stage, frequency, chirality parameter, and the angle of wave incidence.
We propose a new design method for the photonic crystal (PhC) wideband passive optical filters. For this, we join the PhC spectral analysis with investigation of guiding properties of the PhC-waveguides and filters. The method allows improvement of the characteristics of the demultiplexers presented in earlier works, which has been designed by means of photonic band gap maps analysis.
Generation and applications of the optical pulses with a parabolic intensity profile has developed into the area of
dynamic research activity over recent years. Parabolic pulses can propagate remaining their parabolic profile.
Particularly these pulses resist to the deleterious effect of the optical wave breaking. They are of great interest for a
number of applications including the high power pulse generation, and all optical signal processing. Alternative methods
of generating parabolic pulses are of especial interest in the context of non-amplification usage, such as optical
telecommunications. It is found that Gaussian waveforms provide best quasi-parabolic pulses among others and within
shortest distance. There is a range of soliton numbers where the shape of quasi-parabolic pulse is closest to parabolic
one.
We investigate theoretically the influence of indium surface segregation in InGaN/GaN single quantum wells
on its optical properties. 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 indium surface segregation which change selection rules. Quantum well structures having
different indium amount are analyzed and found that the influence of the indium surface segregation on absorption
spectra is more pronounced in quantum well structures with high indium amount.
Spectral characteristics of the interference optical filter based on a free-standing mesoporous silicon film containing
nematic liquid crystal E7 are studied experimentally. The porous structure represents two distributed Bragg reflectors
divided by a quarter-wave microcavity having resonance near 1600 nm. Transmission spectra of the filter are measured
in the temperature range from 27°C to 80°C. For the temperatures less than 62°C (clearing point of the liquid crystal),
we have observed continuous red shift of the microcavity resonant wavelength in the range of 11 nm. Measured thermal
dependence of the shift has sharply increasing slope near the clearing point. For temperatures exceeding 62°C the
microcavity resonant wavelength exhibits slow linear decrease. We have also investigated spectra of the filter using local
heating of the sample with laser. Our studies have shown, that laser beam with power of 100 mW provides total tuning
of the microcavity.
We have investigated a nonlinear pulse reshaping towards parabolic pulses in the passive normal dispersive optical
fibers. We have found that pulses with parabolic intensity profile, parabolic spectrum and linear chirp can be obtained
due to the passive nonlinear reshaping at the propagation distance exceeding a few dispersion lengths. These pulses
preserve parabolic profile during subsequent pulse propagation in a fiber. We have examined the influence of initial
pulse parameters and fiber parameters on the resulted pulse shape.
In the paper, we investigated the bistable properties of the wideband optical filter on the basis of nonlinear 2D
photonic crystal. All-optical flip-flop phenomena have been discovered in such filters which allows switching with
ultra-short pulses. Particularly, the attention in this work is paid to the filter characteristics stability as respect
to radiation parameters variation as well as to production defects.
In this work we investigate the influence of extractor design and temperature on transport properties of quantum
cascade detector. For this purpose we realize numerical calculation of electron lifetimes considering electronphonon
and electron impurities scattering. Electron-phonon interactions are treated using Fermi Golden Rule
which allows to calculate lifetime of carriers with temperature and structure design taking into account. Transport
characteristics of the quantum cascade detectors have been computed using density matrix theory. As a result, we
have obtained the system of ordinary differential equations describing dynamics of electron distribution functions
and intersubband correlations. Managing carrier lifetime in quantum wells gives us possibility to control quantum
efficiency and response.
We propose a new method for mass production of the photonic crystal devices on the basis of widely-known and well-developed technology such as micristructured optical fibers. In this paper, we investigate the optical properties of side-excited microstructured fiber and discuss the conditions for utilization such a structure as planar photonic crystal device, namely, the high-quality resonance filter.
The influence of the geometrical and physical parameters on the photonic band-gap of GaAs and AlGaAs 2D photonic
crystals has been investigated. As a result the gap-maps for geometrical parameters appropriate for operation at around
the λ = 1.5μm wavelength have been obtained, i.e. the wavelength region most widely used in current fibre-optic
telecommunications. Using these gap-maps, it is possible to find the PhC parameters for which the PhC exhibits a PBG
within the telecommunication range.
In the paper, the problem of the effective enhancement of electron capture efficiency has been considered for MQW structures. Different approaches to the problem are used. The most effective one is based on embedding of additional layers in SQH region. We have investigated the influence of such layers on two types of carriers' capture. The first one is the capture of bound carriers from reservoir states in SQH region and the second one is the capture of free carriers from quasi-continuum states. As a result, we have obtained up to tenfold increase of electron capture efficiency.
A numerical model for the investigation of the ultrafast gain properties in asymmetrical multiple quantum-well semi-conductor optical amplifiers (AMQW SOAs) 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.
Self-consistent computations of the potential profile in complex semiconductor heterostructures can be successfully applied for comprehensive simulation of the gain and the absorption spectra, for the analysis of the capture, escape, tunneling, recombination, and relaxation phenomena and as a consequence it can be used for studying dynamical behavior of semiconductor lasers and amplifiers. However, many authors use non-entirely correct ways for the application of the method. In this paper the versatile model is proposed for the investigation, optimization, and the control of parameters of the semiconductor lasers and optical amplifiers which may be employed for the creation of new generations of the high-density photonic systems for the information processing and data transfer, follower and security arrangements. The model is based on the coupled Schrödinger, Poisson's and drift-diffusion equations which allow to determine energy quantization levels and wave functions of charge carriers, take into account built-in fields, and to investigate doped MQW structures and those under external electric fields influence. In the paper the methodology of computer realization based on our model is described. Boundary conditions for each equation and consideration of the convergence for the method are included. Frequently encountered in practice approaches and errors of self-consistent computations are described. Domains of applicability of the main approaches are estimated. Application examples of the method are given. Some of regularities of the results which were discovered by using self-consistent method are discussed. Design recommendations for structure optimization in respect to managing some parameters of AMQW structures are given.
The photonic crystal (PC) coupler and planar photonic band gap (PBG) coupler were theoretically investigated. Also the conventional step-index coupler was investigated for comparison with these couplers. The PC-coupler is a structure formed by the gradual tapering of the photonic-crystal holey fiber and the conventional step-index coupler -- by the gradual tapering of the conventional fiber. The planar PBG-coupler is a planar PC waveguide, in which defect region has taper-like geometry. The photonic crystal couplers are characterized by alternation of the material refractive index along the wave propagation direction, i. e. along the optical axis of the taper. In our investigation an effective refractive index model for two-dimensional photonic crystal was used. This model allows to analyze the waveguide structures, which work on the effective index waveguiding in a defect of the photonic crystal. The optical field in photonic crystal couplers, PBG couplers and conventional couplers was investigated. Also losses and mode shape distortion of all types of the couplers were calculated.
At the present paper the photonic crystal coupler of an optical fiber, which has been made by the adiabatic tapering of the optical fiber based on the photonic crystal is presented. In our investigation an effective refractive index model of two-dimensional photonic crystal was used. This model allows analyzing the waveguide structures, which work on the effective index waveguiding in a defect of the photonic crystal. The effective refractive indexes of such couplers were numerically found. Using this model the field distribution in these couplers were investigated and were calculated its losses. It was shown that the couplers with smaller input diameter and the fixed output diameter have smaller losses.
The semiconductor laser is commonly used as a light source in fiber-optical telecommunication systems. In order to send as much information as possible in a short time, it is important that the laser has a large modulation bandwidth, i.e., the turn-on and turn-off time should be as short as possible. In analogue fiber optic systems for transmission of radio or television signals, it is also important that the light from the laser increases linearly with driving current even at high modulation frequencies. Otherwise, the transmitted signal will become distorted. The modulation bandwidth and the modulation distortion are dependent both on the laser structure and the gain characteristics of the active material. One of the most useful approaches for the time-domain description of the response of optoelectronic devices is the so-called "rate equation model," which has been widely used to describe laser performance. Commonly, laser models with simple gain expressions are used for simulation of laser dynamics. In these models the small-signal dynamic parameters like the differential gain and gain saturation parameter are extracted from modulation response measurements. However, we show that in order to correctly calculate distortion, an accurate model of the dependence of gain on carrier density, n, and photon density, s, is needed. Commonly used gain models, fitted to give exactly the same modulation response can give significantly different distortion behavior.
The aim of this work is to illustrate features of computation for MQW strained semiconductor lasers based on type-I and II heterostructures. The theoretical results founded on the given distinctions allowed to investigate the threshold current temperature dependence and research the behavior of all its components for InGaAsSb/AlGaAsSb and InGaAsSb/GaSb heterolasers which we have chosen as examples of type-I and II heterostructures respectively. The obtained data and additionally carried out computations assure that further threshold current optimization will result in its lowering.
The temperature dependence of the lasing threshold in the GaInAs-GaInAsP-InP bi-quantum-well heterolasers with different widths of the quantum wells (4 and 9 nm) has been determined. Processes of non-radiative Auger recombination which occur in the active region of the quantum-well lasers have been included into consideration. The analytical approach for the evaluation of the characteristic temperature of the lasing threshold is presented. For described asymmetric quantum-well heterostructure lasers, it is shown that the influence of Auger recombination processes on the temperature behavior of the lasing threshold is not essential until the temperature of the active region is lower than 360 K and the cavity losses do not exceed 80 cm-1.
In the present paper the modified effective-index model of photonic-crystal waveguide is proved and presented. This model allows to reduce the three-dimensional numerical analysis to the two-dimensional consideration of the waveguiding due to representing of the waveguide as its step-index analog with the cladding region described by the effective refractive index of two-dimensional photonic crystal (PC) and the effective core size. The effective core size allowing equivalent description of waveguiding properties in the PC waveguide using the modified effective-index model and its numerical approximation are numerically defined. The obtained data have been used for numerical investigation of waveguide couplers formed by tapered photonic crystal fiber (PCF). It was shown that the couplers have smaller loss in comparison with couplers made by tapered step-index fiber.
At the present paper the photonic crystal coupler of an optical fiber, which has been made by the adiabatic tapering of the optical fiber based on the photonic crystal is presented. These couplers are characterizing by material refractive index changing in a spatial direction along of the wave propagation direction. In our investigation an effective refractive index model of two-dimensional photonic crystal was used. This model allows analyzing the waveguide structures, which work on the effective index waveguiding in a defect of the photonic crystal. Also this model allows reducing the investigation time by reducing the three-dimensional numerical analysis of the coupler to the two-dimensional consideration. The effective refractive indexes of such couplers were numerically found. Using this model the field distribution in these couplers were investigated and were calculated its losses. It was shown that the couplers with smaller input diameter and the fixed output diameter have smaller losses.
We present development results of the web-oriented environment for distance education in the field of the semiconductor laser physics. The paper includes description of the Interactive Environment for Distance Education (IEDE) focused on connection of lecture courses and the laser simulation package LaserCAD III, which allows considering lasers directly during reading of lectures via Internet. Some examples of the package using are presented.
Results of numerical investigation of transversal cavity mode influence on static and dynamic characteristics of oxide-confined vertical-cavity surface emitting laser are presented and discussed. It was shown that mode selection could improve modulation properties of laser. Instigated the influence of injection current on near field distribution and spatial hole burning effect.
The given work is devoted to a problem of numerical simulation and analysis of the vertical cavity lasers parameters with the purpose of numerical simulation methods improving. The analysis of the VCSEL with the help of the mathematical model, based on beam propagation method, are presented. The dependence of the VCSEL dynamic behavior on the temperature dependence of the gain coefficient is submitted. With the help of extended system of the rate equations for VCSEL the modulation characteristics are obtained. Analysis of the lasing wavelength dependence on thermal gain coefficient is carried out.
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