Abstract:The energy spectrum and optical absorption of confined carriers in ellipsoidal CdSe quantum dots are calculated. Our model relies on the effective mass approximation and Fermi's golden rule for the electronic structure and optical properties, respectively. We demonstrate that the electronic structure and the interband optical absorption are highly dependent on the ellipsoid aspect ratio.
“…Besides, the time constants of the electron escape process in the conduction and the valence bands are obtained as where is the energy spacing between ES c(v) and GS c(v) 47 – 49 . In addition, and are the electron degeneracy of the ground and excited states in the conduction and the valance band, respectively which is determined by , , , and 50 . The total number of the electrons of each state, GS c , ES c , GS v , and ES v are demonstrated with , , where V d is the volume of the active region and N QD,i is the corresponding QD density for channel-1 and 2, respectively.…”
Section: The Theoretical Modeling Of Two-channel Aommentioning
Recently, all-optical modulators are potentially the most promising candidate to achieve high-bit rate modulation in high-speed all-optical communication technologies and signal processing. In this study, a two-channel all-optical modulator based on a solution-processed quantum dot structure is introduced for two sizes of quantum dots to operate at two wavelengths of MIR spectra (3 µm and 5 µm). To perform numerical and theoretical analysis and evaluate the optical behavior of the proposed all-optical modulator, the coupled rate and propagation equations have been solved by considering homogeneous and inhomogeneous broadening effects. The modulation depth at the 50 GHz frequency and 3 mW probe power is attained, about 94% for channel-1 with the wavelength of 559 nm at 300 Wcm−2 pump power density as well as approximately 83.5% for channel-2 with the wavelength of 619 nm at 500 Wcm−2 pump power density. The introduced two-channel all-optical modulator can operate simultaneously at two wavelengths during the modulation process in which information could be transmitted through both signals from the control light. This approach can present the practical device as a high-contrast and high-speed two-channel all-optical modulator with a high modulation depth in numerous applications such as thermal imaging in night vision cameras, wavelength de-multiplexing, signal processing, free-space communication.
“…Besides, the time constants of the electron escape process in the conduction and the valence bands are obtained as where is the energy spacing between ES c(v) and GS c(v) 47 – 49 . In addition, and are the electron degeneracy of the ground and excited states in the conduction and the valance band, respectively which is determined by , , , and 50 . The total number of the electrons of each state, GS c , ES c , GS v , and ES v are demonstrated with , , where V d is the volume of the active region and N QD,i is the corresponding QD density for channel-1 and 2, respectively.…”
Section: The Theoretical Modeling Of Two-channel Aommentioning
Recently, all-optical modulators are potentially the most promising candidate to achieve high-bit rate modulation in high-speed all-optical communication technologies and signal processing. In this study, a two-channel all-optical modulator based on a solution-processed quantum dot structure is introduced for two sizes of quantum dots to operate at two wavelengths of MIR spectra (3 µm and 5 µm). To perform numerical and theoretical analysis and evaluate the optical behavior of the proposed all-optical modulator, the coupled rate and propagation equations have been solved by considering homogeneous and inhomogeneous broadening effects. The modulation depth at the 50 GHz frequency and 3 mW probe power is attained, about 94% for channel-1 with the wavelength of 559 nm at 300 Wcm−2 pump power density as well as approximately 83.5% for channel-2 with the wavelength of 619 nm at 500 Wcm−2 pump power density. The introduced two-channel all-optical modulator can operate simultaneously at two wavelengths during the modulation process in which information could be transmitted through both signals from the control light. This approach can present the practical device as a high-contrast and high-speed two-channel all-optical modulator with a high modulation depth in numerous applications such as thermal imaging in night vision cameras, wavelength de-multiplexing, signal processing, free-space communication.
“…The first study [3] of the optical properties of a spherical quantum dot with infinitely high walls was a theoretical investigation of the direct absorption of light. The optical properties of nanoparticles having cylindrical, ellipsoidal, semiellipsoidal, pyramidal and lens shape were analysed in subsequent works [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The analysis of both the optical transition-matrix elements and the oscillator strengths in the dipole approximation revealed interesting features induced by the size and shape of a nanoparticle.…”
The optical properties of crystalline semiconductor nanoparticles with ellipsoidal shape are investigated and discussed as a function of the shape-anisotropy parameter. The optical transitionmatrix elements are calculated in the dipole approximation using perturbation theory and with a direct diagonalization of the appropriate Hamiltonian. The matrix elements involving the ground and first excited states are monotonic functions of the shape-anisotropy parameter, whereas matrix elements involving the highly excited states have zeros and extrema that are reflected in the behaviour of the corresponding transition probabilities. Moreover, some matrix elements involving the excited states have discontinuity. We demonstrate that, nanoparticles with ellipsoidal shape can be grown with the infrared as well as ultraviolet features.
“…Optical properties of spheroidal QDs have been studied in 11,12,13,14 . Recently the liquid phase epitaxy technique is used to create ellipsoidal QDs 15,16 .…”
The absorption of light in ellipsoidal quantum dot in the presence of a magnetic field is discussed using perturbation theory. Also the same problem is discussed using the normal modes. Quantum dot absorption coefficient is calculated -as well as threshold frequency of absorption -as a function of applied magnetic field. Theoretical results are compared with experimental data obtained by magneto-luminescence method in In 0.53 Ga 0.47 As quantum dot (M.
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