Browsing by Author "Figueiredo, J. M. L."
Now showing 1 - 10 of 22
Results Per Page
Sort Options
- Chaotic dynamics in resonant tunneling optoelectronic voltage controlled oscillatorsPublication . Romeira, Bruno; Figueiredo, J. M. L.; Ironside, C. N.; Slight, Thomas JamesA new way of generating electrical and optical chaotic carriers is demonstrated using an optoelectronic voltage controlled oscillator consisting of a laser diode (LD) driven by a resonant tunneling diode (RTD) perturbed by radio-frequency signals. The high-dimensional broadband (gigahertz-wide) chaotic current produced by the RTD modulates a LD, providing a simple way to convert electrical chaotic signals into optical subcarriers that can be transmitted by conventional optical channels. Since the chaotic current and the chaotic optical subcarriers are controlled accurately and reproducibly by the RTD, we anticipate this concept can be used as the core of a compact, simple, and low-power consumption optical chaos generator for optical communications.
- Coherent approach to transport and noise in double-barrier resonant diodesPublication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.We implement a quantum approach which includes long range Coulomb interaction and investigate current voltage characteristics and shot noise in double-barrier resonant diodes. The theory applies to the region of low applied voltages up to the region of the current peak and considers the wide temperature range from zero to room temperature. The shape of the current voltage characteristic is well reproduced and we confirm that even in the presence of Coulomb interaction the shot noise can be suppressed with a Fano factor well below the value of 0.5. This feature can be an indication of coherent tunneling since the standard sequential tunneling predicts in general a Fano factor equal to or greater than the value 0.5. This giant suppression is a consequence of Pauli principle as well as long range Coulomb interaction. The theory generalizes previous findings and is compared with experiments.
- Current noise in resonance tunnel diodes based on InGaAlAs heterostructuresPublication . Figueiredo, J. M. L.Noise in resonance tunnel diodes based on InGaAlAs structures is studied at two frequencies. A shot noise caused by the current flowing through two barriers of the heterostructure is identified. It was found that if the voltage across the structure is within the first ascending section of the current–voltage characteristics, the shot noise is suppressed with the suppression ratio G ~ 1/15. In the second ascending section of the current– voltage characteristic, the shot noise coincides with the shot noise of electrons passing through one barrier ( G = 1) by the order of magnitude. The specific features of current flow affecting the behavior of noise in the resonance tunnel structures are discussed.
- DC characterization of tunnel diodes under stable non-oscillatory circuit conditionsPublication . Wang, Liquan; Figueiredo, J. M. L.; Ironside, C. N.; Wasige, EdwardA common problem in designing with Esaki tunneling diodes in circuits is parasitic oscillations, which occur when these devices are biased in their negative differential resistance(NDR) region. Because of this, the measured current–voltage(I–V )characteristics in the NDR region are usually incorrect, with sudden changes in current with voltage and a plateaulike waveform in this region. Using a full nonlinear analysis of the shunt-resistor-stabilized tunnel diode circuit, we have established the criteria for the range of element values that give stable operation. On this basis, I–V measurement circuits can be designedto be free from both low-frequency bias oscillations and highfrequency oscillations. The design equations lead to a direct I–V measurement setup in which the stabilization resistor in series with a capacitor can be employed. Experimental results validate the approach, and this is confirmed by second-derivative analysis (d2I/dV 2) of the measured I–V characteristics.
- Electric field switching in a resonant tunneling diode electroabsorption modulatorPublication . Figueiredo, J. M. L.; Ironside, C. N.; Stanley, C. R.The basic mechanism underlying electric field switching produced by a resonant tunneling diode (RTD) is analyzed and the theory compared with experimental results; agreement to within 12% is achieved. The electroabsorption modulator (EAM) device potential of this effect is explored in an optical waveguide configuration. It is shown that a RTD-EAM can provide significant absorption coefficient change, via the Franz– Keldysh effect, at appropriate optical communication wavelengths around 1550 nm and can achieve up to 28-dB optical modulation in a 200- m active length device. The advantage of the RTD-EAM over the conventional reverse-biased p–n junction EAM, is that the RTD-EAM has, in essence, an integrated electronic amplifier and, therefore, requires considerably less switching power.
- Giant suppression of shot noise as signature of coherent transport in double barrier resonant diodesPublication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.Shot noise suppression in double barrier resonant tunnelling diodes with a Fano factor well below the value of 0.5 is theoretically predicted. This giant suppression is found to be a signature of the coherent transport regime and can occur near zero temperature as a consequence of the Pauli principle or above about 77 K as a consequence of long range Coulomb interaction. These predictions are validated by experimental data.
- Giant suppression of shot noise in double barrier resonant diode: a signature of coherent transportPublication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.Shot noise suppression in double barrier resonant tunnelling diodes with a Fano factor well below the value of 0.5 is theoretically predicted. This giant suppression is found to be a signature of coherent transport regime and can occur at zero temperature as a consequence of the Pauli principle or at sufficiently high temperatures above 77 K as a consequence of a long-range Coulomb interaction. These predictions are in agreement with experimental data.
- Integration of a RTD with an optical waveguide to form a high speed electroabsorption modulatorPublication . Figueiredo, J. M. L.; Ironside, C. N.; Leite, A. M. P.; Stanley, C. R.High speed Optoelectronic modulation using the resonant tunnelling characteristics by interaction of a resonant tunnelling diode (RTD) in the middle of an unipolar ridge optical waveguide based on the GaAs/AlGaAs system is investigated. This interaction of an RTD within an optical waveguide introduces high non-linearities into the electrical characteristics of the waveguide by inducing large electric field changes on the collector region which give rise to a band-edge shift via the Franz-Keldysh effect that can be used for electroabsorption modulation up to millimeter-wave frequencies of light at photon energies close to the bandgap energy of the semiconductor, in this case around 900 nm. The device allows efficient high speed intensity modulation requiring a few hundreds of mV as drive voltage. Streak camera studies have shown around 4 dB modulation depth at 14 GHz for an applied voltage at 1 GHz of around 0.4 V, implying a bandwidth-to-voltage ratio of 33 GHz/V.
- A liénard oscillator resonant tunnelling diode-laser diode hybrid integrated circuit: model and experimentPublication . Slight, Thomas James; Romeira, Bruno; Wang, Liquan; Figueiredo, J. M. L.; Wasige, Edward; Ironside, C. N.We report on a hybrid optoelectronic integrated circuit based on a resonant tunnelling diode driving an optical communications laser diode. This circuit can act as a voltage controlled oscillator with optical and electrical outputs. We show that the oscillator operation can be described by Liénard’s equation, a second order nonlinear differential equation, which is a generalization of the Van der Pol equation. This treatment gives considerable insight into the potential of a monolithic version of the circuit for optical communication functions including clock recovery and chaotic source applications.
- Modeling of light-sensitive resonant-tunneling-diode devicesPublication . Coelho, I. J. S.; Figueiredo, J. M. L.; Ironside, C. N.We present a method to include the effects of light excitation on two different models of resonant-tunneling-diode-based devices. Our approach takes into account both photoconductive and charge accumulation effects responsible for shifting the static I –V curve when the structure is under light excitation. Computational simulations led to good agreement between the model and experimental results
- «
- 1 (current)
- 2
- 3
- »