Sharif Digital Repository

We present an edge emitting laser structure employing silicon carbide polymers only. In this structure, 3C-SiC well embedded in 6H-SiC barriers are used as the active region, which is sandwiched between the 6H-SiC mirror at the top and bottom of structure. The basic design goal is to use only silicon carbide polymers and decrease the threshold current and stable optical wavelength of the lasers with silicon carbide polymers. This paper provides key results of the device characteristics, including the light power versus electrical current and the optical wavelength versus current  

In the present work, a new structure of the strained quantum-well (QW) laser diode is designed and simulated. In this structure, the active region consists of tow 6H-SiC barrier and 3C-SiC quantum well (QW)which is sandwiched between two layers of 6H-SiC that can be interpreted in terms of a type-II heterostructure character and a built-in electric field due to the pyroel ectricity of 6H using an industrial-based numerical simulator. The basic design goal was to decrease the threshold current by using only silicon carbide polymers. We could obtain a working model at stable optical wavelength of 0.83μm. This paper provides key results of the device characteristics, including the light power... 

In the present paper, we investigated the various elements of heat sources within a silicon carbide polymers (6H-SiC and 3C-SiC) semiconductor laser. The device employs 3C-SiC quantum well (QW) which is sandwiched between two layers of 6H-SiC as cladding regions that can be interpreted in terms of a type-II heterostructure character and a built-in electric field due to the pyroelectricity of 6H using a numerical simulator. The basic design goal was the study of the various elements of heat sources, including the Joule heat power, the Peltier-Thomson heat power and the recombination heat power  

In this paper, we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analyze is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporate the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

In this paper we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analysis is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporates the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using... 

We have performed an analysis of harmonic contents of the optical output power for a diode laser and described the results in details. In the first step the absolute value of power for each harmonic is obtained in terms of various diode laser parameters, and the variations of external parameters such as modulation current, bias current and frequency are discussed. The analysis is done by direct solution of rate equations of an arbitrary diode laser for carrier and photon densities. We conclude that the maximum power occurs at isolated peaks and their loci have been investigated and shown to be predictable by theory. It is known that the optical power has a nonlinear dependence on frequency,... 

Large signal behavior of the Laser Diode is analyzed with the aim of finding a qualitative relationship between modulation amplitude and the change in the shape of its transfer function. It is found that, at quasi-static conditions, increasing the amplitude of the modulating signal smoothes out the original piecewise-linear transfer function of the diode. It further shifts the now smoothed knee point to lower DC currents. As the frequency increases, however, these effects become less and less pronounced. In addition, the transfer function becomes rather wavy due to the failure of current density to reach the saturation level necessary for adequate stimulated emission. At even higher... 

Using a simple nonlinear model based on rate equations, and by employing a harmonic balance method, we develop a theory of optimal mixing in directly modulated semiconductor laser diodes. We perform a consistent numerical solution to the mixing in laser diodes to the arbitrary accuracy and intermodulation index (m, n). Through numerical computations we demonstrate that there is an optimal bias in mixing, corresponding to a relaxation frequency, fr, coinciding with the subcarrier frequency, f1, at which the mixing power is maximized nearly simultaneously for all intermodulation products, fmn. In terms of increasing the signal's current amplitude, it will be shown that it would result in a... 

The electric field of the modes of semiconductor microring lasers (SMRLs) in the presence of bus waveguide reflections are linear combinations of the clock wise (CW) and the counter clock wise (CCW) electric fields. The mode structures can be controlled by the waveguide reflection coefficients. The power ratio and phase difference of the CW and CCW fields of one mode is proportional to the ratio of the reflection coefficients of the left and right waveguides. It is shown that the degenerate CW and CCW modes in the presence of bus waveguide reflections are split into two modes with different frequencies. Employing these new modes, SMRL can be used as an element to design flip-flops used in... 

In practice, photoacoustic (PA) waves generated with cost-effective, low-energy laser diodes, are weak and almost buried in noise. Reconstruction of an artifact-free PA image from noisy measurements requires an effective denoising technique. Averaging techniques are widely used to increase the signal-to-noise ratio (SNR) of the weak PA signals but the process is time-consuming and in case of very low SNR measurements, hundreds/thousands of data acquisition epochs needed to provide the required data In this study, we propose to use adaptive denoising methodology in which adaptive line enhancers (ALE) has been embedded for increasing the SNR of PA signals in very low-cost PA systems. Our... 

The synergistic effect of plasmonic Au-Ag nanoparticles (NPs) on the increase of absorption band of nano-sized TiO2 and magnetic property of Fe3O4 NPs on the separation-ability of this semiconductor was applied for preparation of eight magneto-plasmonic photocatalysts for degradation of rhodamine-6G (Rh6G) in textile wastewater. The size, structure, morphology, crystallinity and optical and magnetic properties of prepared photocatalysts have been evaluated by various characterization techniques. Their photocatalytic activities were assessed under irradiation of an intense linear 405-nm laser and a continuous solar-simulated xenon lamp. The results were demonstrated that in comparison to the... 

Reduced graphene oxide nanomeshes (rGONMs), as p-type semiconductors with band-gap energy of ~1. eV, were developed and applied in near infrared (NIR) laser stimulation of human neural stem cells (hNSCs) into neurons. The biocompatibility of the rGONMs in growth of hNSCs was found similar to that of the graphene oxide (GO) sheets. Proliferation of the hNSCs on the GONMs was assigned to the excess oxygen functional groups formed on edge defects of the GONMs, resulting in superhydrophilicity of the surface. Under NIR laser stimulation, the graphene layers (especially the rGONMs) exhibited significant cell differentiations, including more elongations of the cells and higher differentiation of...