In this work, a bidirectional grating coupler for perfectly vertical coupling is proposed. The coupling efficiency is enhanced using a silicon nitride (Si₃N₄) layer above a uniform grating. In the presence of Si₃N₄ layer, the back-reflected optical power into the fiber is diminished and coupling into the waveguide is increased. Genetic algorithm (GA) is used to optimize the grating and Si₃N₄ layer simultaneously. The optimal design obtained from GA shows that the average in-plane coupling efficiency is enhanced from about 57.5% (−2.5 dB) to 68.5% (−1.65 dB), meanwhile the average back-reflection in the C band is reduced from 17.6% (−7.5 dB) to 7.4% (−11.3 dB). With the help of a backside metal mirror, the average coupling efficiency and peak coupling efficiency are further increased to 87% (−0.6 dB) and 89.4% (−0.49 dB). The minimum feature size of the designed device is 266 nm, which makes our design easy to fabricate through 193 nm deep-UV lithography and lowers the fabrication cost. In addition, the coupler proposed here shows a wide-band character with a 1-dB bandwidth of 64 nm and 3-dB bandwidth of 96 nm. Such a grating coupler design can provide an efficient and cost-effective solution for vertical fiber-to-chip optical coupling of a Wavelength Division Multiplexing (WDM) application.

In the photovoltaic (PV) field, the outdoor evaluation of a PV system is quite complex, due to the variations of temperature and irradiance. In fact, the diagnosis of the PV modules is extremely required in order to maintain the optimum performance. In this paper, an artificial neural network (ANN) is proposed to build and train the model, and evaluate the PV module performance by mean bias error, mean square error and the regression analysis. We take temperature, irradiance and a specific voltage for input, and a specific current value for output, repeat several times in order to obtain an I-V curve. The main feature lies to the data-driven black-box method, with the ignorance of any analytical equations and hence the conventional five parameters (serial resistance, shunt resistance, non-ideal factor, reverse saturation current, and photon current). The ANN is able to predict the I-V curves of the Si PV module at arbitrary irradiance and temperature. Finally, the proposed algorithm has proved to be valid in terms of comparison with the testing dataset.

Low power and ultrafast multi-state storage resistive switching memory (RRAM) device had been developed based on Al/Al2O3/AlxOy/Al structure. Both of Al2O3 and Al nanocrystal (nc-Al) induced AlxOy thin films were deposited by RF sputtering. The nc-Al AlxOy based RRAM device showed typical unipolar switching behavior which was due to conductive filaments (CFs) connected and broke in Al2O3/AlxOy layers. An additional 30 nm Al2O3 thin film would deposit on AlxOy film to form bi-layer structure, in which the multi-state switching could be observed by applying different voltage pulses on it. In this study, a 15 V pulse with 600 ps width could trigger RRAM device switch from high resistance state (HRS) to next intermediate resistance state (IRS), the device could finally switch to LRS after continuous pulse simulation. Such switching from HRS to LRS was called “writing” process as data would be stored in RRAM device after this process. A longer but lower amplitude voltage pulse was required to make device switch from LRS to HRS which was called “erasing” process, as data would be eliminated after this process. The multi-state switching was corresponding internal switching between these IRSs during “writing” and “erasing” process. The multi-level resistances might be caused by partially formed CFs in Al2O3/AlxOy layers. The distribution of CFs could be controlled by controlling the shape of pulse voltage to achieve this multi-state storage. This bilayer structured RRAM device had good endurance and retention performances at both room and high temperatures.

We propose a broadband high-efficiency grating coupler for perfectly vertical fiber-to-chip coupling. The up-reflection is reduced, hence enhanced coupling efficiency is achieved with the help of a Fabry-Perot-like cavity composed of a silicon nitride reflector and the grating itself. With the theory of the Fabry-Perot cavity, the dimensional parameters of the coupler are investigated. With the optimized parameters, up-reflection in the C-band is reduced from 10.6% to 5%, resulting in an enhanced coupling efficiency of 80.3%, with a 1-dB bandwidth of 58 nm, which covers the entire C-band. The minimum feature size of the proposed structure is over 219 nm, which makes our design easy to fabricate through 248 nm deep-UV lithography, and lowers the fabrication cost. The proposed design has potential in efficient and fabrication-tolerant interfacing applications, between off-chip light sources and integrated chips that can be mass-produced.

This study deals with the CdS/CdTe solar cells under low illumination intensity, with cell #1 for the shunt resistance exceeding 100,000 Ω·cm² and cell #2 for the shunt resistance above 1000 Ω·cm². The diode parameter variations with the decline of the irradiance intensity are illustrated by dividing 0–100 mW/cm⁻² into a number of small intensity ranges for J–V measurements and assuming the diode parameters to be constant within each range, the diode parameters of each range including the series resistance, the shunt resistance, the reverse saturation current density and the ideality factor are then extracted by employing an analytical approach. The mechanism of the cell performance deviations are also investigated by basic theories, reports and experiments. For cell #1 with higher R_sh corresponding to less traps, R_sh shows a upward tendency as the irradiance declines, n and J₀ exhibit a rise with the irradiance and keep nearly unchanged at the low irradiance values mainly due to recombination and carrier contributions, R_s shows a slight increase when the irradiance intensity goes down because of the resistance of CdTe absorption layer. For cell #2 with lower R_sh corresponding to more traps, with the decrease of the illumination intensity, R_sh increases sharply only for captured carrier reduction, R_s goes steadily up similarly, n and J₀ exhibit a decline with the irradiance due to recombination shift. It should be pointed out that R_s varies much smoother than the traditional approximation of a reciprocal of differential at short circuit, and the distribution of R_sh is diverse, and an average R_sh of for each intensity range can reflect the variation trend.