In this paper we simulate and analyze a sample of slow light semiconducting device with quantum dot structure based on coherent population oscillation (CPO). The simulation is conducted to enhance the main parameters of slow light device and a method is presented for setting the output specifications of this kind of devices. In this paper, we deal with changing the size of quantum dot to find the ideal size. The simulation results indicate that as the size of quantum dot changes properly (with reducing more than 50 percent of quantum dots both radius and height), then the slope of diagram of the real part of refractive index increases significantly so that the Slow Down Factor (SDF) predicted to be18 times greater. Analysis and simulations based on cylinderical quantum dots structure slow light devices based on exitonic cpo.
In this paper we simulate and analyze a sample of slow light semiconducting device with quantum dot structure based on coherent population oscillation (CPO). The simulation is conducted to enhance the main parameters of slow light device and a method is presented for setting the output specifications of this kind of devices. In this paper, we deal with changing the size of quantum dot to find the ideal size. The simulation results indicate that as the size of quantum dot changes properly (with reducing more than 50 percent of quantum dots both radius and height), then the slope of diagram of the real part of refractive index increases significantly so that the Slow Down Factor (SDF) predicted to be18 times greater. Analysis and simulations based on cylinderical quantum dots structure slow light devices based on exitonic cpo.
In this paper we analyze the structure of two types of quantum dots slow light devices. The first model is slow light devices based on coherent population oscillation (CPO), in this method, slow light device has a pump and signal, the simulation results in the form of curves with refractive index, absorption and slow down factor based on detuning changes is estimated. In the second model, with tunneling induced transparency (TIT) method, slow light device has an electric voltage. The simulation results in the form of curves with refractive index, absorption and Vg/C based on alteration photon energy is plotted. For better comparison with CPO method, in the next step, SDF curve is plotted for slow light device based on TIT. According to this figure, it can be realized that the amount of SDF for slow light using TIT are much higher than the amount of SDF for slow light using CPO. And finally we obtained maximum SDF variations as a function of radius of quantum dots, for both methods. According to this curve, when radius is 4 nm, SDF with slow light device based on TIT, 76 times higher than SDF with slow light device based on CPO and it can be noticed that the maximum SDF and radius of quantum dots, has reverse proportion.
This paper theoretically investigates the effects of changing external magnetic field intensity on exciton binding energy and center frequency in Quantum Dot (QD) slow light devices. The physical size alterations including quantum dot radius and height on the optical characteristics of this device will also be studied. Finally, by variations of both the abovementioned items (magnetic applied field and device sizes), we will predict new properties for the device. Material of the quantum dot (QD) slow light device is made from InGaAs/GaAs and basically works by the coherent population oscillations (CPO) method. Optical properties such as exciton binding energy and center frequency can be tuned and improved using several methods that are discussed in this paper. These methods may be used for optical modulation, signal processing, switching and optical communications. According to the results of our investigation, binding energy may be estimated at the range of 0.02 electron-volts and central frequency of the QD slow light device can be modified in the range of 5 THz.
This paper demonstrates the effects of applying magnetic and electric fields and physical dimensions alterations on AlGaAs/GaAs multiple quantum well (QW) slow light devices. Physical parameters include quantum well sizes and number of quantum wells. To the best of our knowledge, this is the first analysis of the effects of both applying magnetic/electric fields and physical parameters alterations and the first suggestion for matching the prefabrication and post fabrication tuning of the slow light devices based on excitonic population oscillations. The aim of our theoretical analysis is controlling the optical properties such as central frequency, bandwidth, and slow down factor (SDF) in slow light devices based on excitonic population oscillation to achieve better tuning. To reach these purposes, first we investigate the quantum well size and number of quantum wells alteration effects. Next, we analyze the effects of applying magnetic and electric fields to the multiple quantum well structure, separately. Finally, physical parameters and applied external fields are changed for measuring frequency shift and SDF for coherent population oscillation slow light devices. The results show the available central frequency shifts in about 1.6 THz at best. Also the SDF value improvement is about one order of magnitude. These results will be applicable for optical nonlinearity enhancements, all-optical signal processing, optical communications, all-optical switches, optical modulators, and variable true delays.
This article investigates and improves optical properties of slow light devices. The device structure consists GaAs/AlGaAs [110] strained quantum wells (QWs) based on V-type electromagnetically induced transparency (EIT). In this paper, we use an analytical model in fractional dimension in order to simulate and analysis slow light device. Effects of well width variation have been investigated on exciton oscillator strength (EOS) and fractional dimension parameter. Influences of these parameters alterations have been illustrated in optical properties of slow light system such as slow down factor (SDF) and central energy of the device. Based on obtained results, we can adjust optical variables of slow light system with controlling the well thickness. Using proposed method, we have also estimated the maximum value of SDF about 9×103.
Coherent population oscillation (CPO) is a successful method used to implement semiconductorbased slow light using the coherent pump-probe effect. The first demonstration was carried out in semiconductormultiple quantumwells (MQWs) [1-3] soon after the experimental demonstration of slow light in ruby crystal [4,5]. Later, slow light based on CPO in semiconductor QWs and quantum dots (QDs)was also successfully demonstrated at room temperature [6-10], and the slow-light regime was soon extended to the corresponding fast-light regime in semiconductor gainmedia [11-17] using a semiconductor optical amplifier (SOA) alone or combined with an electroabsorbtion (EA) section. The basicworking principle of slow light based onmost pump-probe schemes is to decrease the group velocity vg using the sharp variation of the refractive index ∂n′/∂ω within a narrow frequency range: vg = c ng = c n′ + ω ∂n′ , (2.1) where ng = n′ + ω∂n′/∂ω is the group index n′ is the real part of the refractive index n For the CPO case, the required sharp variation of the refractive index originates from the population oscillation induced by the pump and probe signals applied to a two-level system, as indicated in Figure 2.1. The induced population oscillation generates a new polarization component and changes the susceptibility and thus the refractive index experienced by the signal. In semiconductor quantum structures, this two-level system can be the heavy-hole (HH) exciton [1-3,6,18] of QWs and QDs, or the valence and conductionground states of QDs [18,19]. In principle, as long as the optical transition between the two states is dipole-allowed, the slow light based on CPO can be implemented.
Coherent population oscillations (CPO) in quantum dots (QDs) have been utilized in this article to achieve slow and fast light effects in a semiconductor optical amplifier. These phenomena have been achieved based on a pump-probe scheme and tuning the input current source. Coupled rate equations have been developed to determine the carrier dynamics and occupation probabilities. The effects of barrier, wetting layer and excited state densities have been included for CPO phenomenon occurring between the ground states. A quantum disc model embedded in another disc has been assumed for modeling the QDs and density matrix elements are used to obtain induced polarization at the signal frequency after determining the energy states and state probabilities. Tunable absorption dip, corresponding refractive index variation and group index, exhibit widely tunable slow and fast light characteristics by changing the bias condition.