International Journal of

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CSs have been theoretically predicted and recently experimentally demonstrated in broad area, vertical cavity driven semiconductor lasers (VCSELs) slightly below the lasing threshold. Above threshold, the simple adiabatic elimination of the polarization variable is not correct, leading to oscillatory instabilities with a spuriously high critical wave-number. To achieve real insight on the complete dynamical problem, we study here the complete system of equations and find regimes where a Hopf instability, typical of lasers above threshold, affects the lower intensity branch of the homogeneous steady state, while the higher intensity branch is unstable due to a Turing instability. Numerical results obtained by direct integration of the dynamical equations show that writable/erasable CSs are possible in this regime, sitting on unstable background

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In this paper we consider electromagnetic field quantization in the presence of a dispersive and absorbing semiconductor quantum dot. By using macroscopic approach and Green's function method, quantization of electromagnetic field is investigated. Interaction of a two-level atom , which is doped in a semiconductor quantum dot, with the quantized field is considered and its spontaneous emission rate is calculated. Comparing with the same condition for an excited atom inside the bulk, it is shown that the spontaneous emission rate of an atom will decrease.

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In this paper, considering optical feedback as an optical injection, and taking in to account round-trip time role in the external cavity, a standard small signal analysis is applied on laser rate equations. By considering the relaxation oscillation (f2) and external cavity frequencies (f) ratio for semiconductor laser, field amplitude response gain, optical phase and carrier number for long external cavities (LEC) and short external cavities (SEC) are obtained. Laser output intensity and resonance peak dynamics have been shown by bifurcation diagrams. Furthermore, the effects of some control parameters, such as enhancement factor, pumping current and feedback strength, on response gain have been discussed in short and long external cavities. As a result, in optical injection, for SEC, compared to LEC, more varied dynamics are observed. Also, higher values of the response gain peak in SEC, in comparison with LEC, make SEC to be affected more by the injected beam. SEC provides greater bandwidth, and also better performance in the range of compared to LEC.

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This paper investigates the amount of doping concentration in silicon semiconductor using optical principle.  Both donor and acceptor impurities of n type and p-type silicon semiconductor materials are computed at wavelength of 1550 nm. During the computation of donor and acceptor impurities, both reflection and absorption losses are considered. Theoretical result showed that transmitted intensity through both n-type and p-type silicon structure increases with respect to doping concentration (10¹⁵ cm^-3 to 10²¹ cm^-3). It is also seen that transmitted intensity increases slowly up to 10²⁰ cm^-3 and then increases rapidly with the increase of doping concentration. Finally an experimental set up is proposed to estimate the doping concentration in silicon semiconductor.

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We present the procedure for designing a high speed and low power all-optical analog to digital converter (AO-ADC), by integrating InGaAsP semiconductor optical amplifier (SOA) with InP based photonic crystal (PhC) drop filters. The self-phase modulation in the SOA can shift the frequency of the Gaussian input pulse. The two output PhC based drop filters are designed to appropriately code the frequency-shifted analog signals by the SOA, converting them to four desired digital output levels. Our numerical results show that in an appropriately designed AO-ADC, the center wavelength (1572 nm) of an amplitude modulated Gaussian pulse of 1.8 ps width and 1.56 pJ energy can be shifted by 6.7 nm, by the SOA, and then be quantized and coded to four digital levels (00, 01, 10, and 11). The two point-defect PhC drop filters, compensating the effect of the frequency shift by SOA, minimize the AO-ADC integral and differential nonlinearity errors.

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In this work, the effect of changing the dimensions of the layer structure on the collection of electrical charge carriers which been produced in the thin film composed of P3HT[1] and PCBM[2] that is between two electrodes, using the Monte Carlo numerical simulation with Bortez, Callus and Lebowitz algorithms, with checkered structure and different dimensions 60×15×5 sites, 60×30×5 sites, have been the conditions of the layers. At first, the average number of electrons and holes produced on the cathode and anode electrodes in two stages (simultaneous injection of excitons, without and with the presence of deep traps) was calculated and it was concluded that, by increasing layer width, the average number of electrical charge carriers collected on the electrodes has decreased, which has a direct impact on production of layer circuits and solar cell performance. Finally, the amount of external quantum efficiency of the layers was also calculated. In 60×15×5 sites layer, in two stages – without and with the presence of traps – the average value of external quantum efficiency 52.3% and 42.43% was obtained and in 60×30×5 sites layer, the value of 42.43% and 37.9% was calculated.

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We theoretically analyze the sensing properties of a one-dimensional photonic crystal-based biosensor for detecting cancer cells infiltrated in a defect cavity layer. The biosensor consists of a sample cavity layer sandwiched between two identical photonic crystals of Hgba₂Ca₂Cu₃O_8+d and GaAs. We use the transfer matrix method to evaluate the performance of the biosensor. We show that a defect mode appears in the transmission spectrum of the biosensor that its position depends on the type of cancer cells in the cavity layer. The analysis is carried out by comparing the transmittance peaks of the cancer cells with the normal cells. We investigate the performance of the biosensor under different hydrostatic pressures and temperatures. We show that one can use temperature change to fine-tune the frequency of the defect modes. In addition, we can adjust the working area of the biosensor by changing the hydrostatic pressure. It is shown that the sensitivity of the biosensor is independent of the temperature, while it strongly depends on the hydrostatic pressure.

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In this article, the conditions of pulse production in two mutually coupled lasers are studied. Based on the obtained characteristic equation and its roots, the dynamical behavior of the system and the threshold of the instability are analyzed. For the stable operation of the system and with the use of the time series curves, it is possible to study the dynamical behavior and the stability ranges of the laser in the presence of the saturable absorber and the gain environment. This paper aims to achieve from quasi-periodic behavior in a solitary laser to the generation of a pulse train from two mutually coupled lasers in the presence of saturable absorbers. Also, the stability range for a solitary laser and then for two coupled lasers in the presence of saturable absorbers have been studied.