In this paper, an electrically driven optical modulator and switch based on micro-ring resonators using the phase change material (PCM) of G e 2 S b 2 T e 5 (GST) is designed and their optical properties are investigated. The change in refractive index between two states in PCMs is orders of magnitude larger than conventional electro-optic and free-carrier dispersion effects. These extraordinary variations make PCMs excellent candidates for optical active devices such as modulators and switches. In our design, GST is used as the active material because it is far more stable and results in lower insertion loss compared to other PCMs such as vanadium dioxide ( V O 2 ) (at λ = 1.55 µ m , the imaginary part of the refractive index is 1.49 for GST and 2.53 for V O 2 is their metallic phases). By optimizing the GST dimensions, the device figure of merit is maximized. Three-dimensional finite-difference time-domain simulations show a very high extinction ratio of 37.3 dB with a low insertion loss of 0.427 dB for the proposed modulator and high extinction ratios of 19 dB and 10 dB in off and on states and insertion losses of 1.52 dB and 2.02 dB in off and on states, respectively, of the proposed 1 × 2 switch.

We present a physical model to study of dark current and noise characteristics of quantum dot infrared photodetectors (QDIPs). This model considers both carriers thermoexcitaion and carriers' field-assisted tunneling which are main origin of dark current and noise in QDIPs. We use this model to analyze effect of different structural parameters such as QDs lateral size and density of QD, and environmental parameters such as bias voltage and operating temperature on the dark current and noise of QDIP. Theoretical results obtained from our model are in excellent agreement with reported experimental data. Therefore, the validity of the model is proven for these reasons. This model can be extended to other quantum structure detectors to evaluate noise and dark current characteristics.

In this paper, a design for a high extinction ratio Mach–Zehnder optical modulator is proposed. The switchable refractive index of the germanium-antimony-selenium-tellurium (GSST) phase change material is employed to induce destructive interference between the waves passing through Mach–Zehnder interferometer (MZI) arms and to realize amplitude modulation. A novel, to the best of our knowledge, asymmetric input splitter is designed for the MZI to compensate for unwanted amplitude differences between MZI arms and increase the modulator performance. Three-dimensional finite-difference-time-domain simulations show a very high extinction ratio (ER) and low insertion loss (IL) of 45 and 2 dB, respectively, for the designed modulator at the wavelength of 1550 nm. Moreover, the ER is above 22 dB, and the IL is below 3.5 dB in the wavelength range of 1500–1600 nm. The thermal excitation process of GSST is also simulated using the finite-element method, and the speed and energy consumption of the modulator are estimated.

Reduction of dark current at high-temperature operation is a great challenge in conventional quantum dot infrared photodetectors, as the rate of thermal excitations resulting in the dark current increases exponentially with temperature. A resonant tunneling barrier is the best candidate for suppression of dark current, enhancement in signal-to-noise ratio, and selective extraction of different wavelength response. In this paper, we use a physical model developed by the authors recently to design a proper resonant tunneling barrier for quantum infrared photodetectors and to study and analyze the spectral response of these devices. The calculated transmission coefficient of electrons by this model and its dependency on bias voltage are in agreement with experimental results. Furthermore, based on the calculated transmission coefficient, the dark current of a quantum dot infrared photodetector with a resonant tunneling barrier is calculated and compared with the experimental data. The validity of our model is proven through this comparison. Theoretical dark current by our model shows better agreement with the experimental data and is more accurate than the previously developed model. Moreover, noise in the device is calculated. Finally, the effect of different parameters, such as temperature, size of quantum dots, and bias voltage, on the performance of the device is simulated and studied.

No abstract