Modeling for Single-Photon Avalanche Diodes: State-of-the-Art and Research Challenges.

With the growing importance of single-photon-counting (SPC) techniques, researchers are now designing high-performance systems based on single-photon avalanche diodes (SPADs). SPADs with high performances and low cost allow the popularity of SPC-based systems for medical and industrial applications. However, few efforts were put into the design optimization of SPADs due to limited calibrated models of the SPAD itself and its related circuits. This paper provides a perspective on improving SPAD-based system design by reviewing the development of SPAD models. First, important SPAD principles such as photon detection probability (PDP), dark count rate (DCR), afterpulsing probability (AP), and timing jitter (TJ) are discussed. Then a comprehensive discussion of various SPAD models focusing on each of the parameters is provided. Finally, important research challenges regarding the development of more advanced SPAD models are summarized, followed by the outlook for the future development of SPAD models and emerging SPAD modeling methods.

Numerical Analysis of MIM-Based Log-Spiral Rectennas for Efficient Infrared Energy Harvesting.

This work presents the design and analysis of a metal-insulator-metal (MIM)-based optical log spiral rectenna for efficient energy harvesting at 28.3 THz. To maximize the benefits of the enhanced field of the proposed nano-antenna in the rectification process, the proposed design considers the antenna arms (Au) as the electrodes of the rectifying diode and the insulator is placed between the electrode terminals for the compact design of the horizontal MIM rectenna. The rectifier insulator, Al2O3, was inserted at the hotspot located in the gap between the antennas. A detailed analysis of the effect of different symmetric and asymmetric MIM-configurations (Au-Al2O3-Ag, Au-Al2O3-Al, Au-Al2O3-Cr, Au-Al2O3-Cu, and Au-Al2O3-Ti) was conducted. The results of the study suggested that the asymmetric configuration of Au-Al2O3-Ag provides optimal results. The proposed design benefits from the captured E-field intensity, I-V, resistivity, and responsivity and results in a rectenna that performs efficiently.

Optimized polarization-independent Chand-Bali nano-antenna for thermal IR energy harvesting.

A novel, polarization-independent, wide-angle reception Chand-Bali nano-antenna is proposed. An adjoint-based optimization algorithm is used to create the same resonance at both linear polarizations of the incident radiation. The nano-antenna optimal parameters reveal that two hot spots with a strong field enhancement are created. These hot-spots could be integrated with metal-insulator-metal (MIM) diodes to form a rectenna for infrared (IR) energy harvesting. The metallic resonators allow for selecting several materials to facilitate the fabrication of the nano-antenna and the MIM diode. The Chand-Bali-based IR rectennas are investigated and simulations demonstrate an improvement of more than one order of magnitude in efficiency compared to ones using traditional nano-antennas.

Wide-angle, wide-band, polarization-insensitive metamaterial absorber for thermal energy harvesting.

We propose a wide-band metamaterial perfect absorber (MPA), using the coupling in the near-field of a quadruple split-ring resonator concentric with crossed ellipses. We designed the MPA with a metal-insulator-metal (MIM) structure for use in thermal energy harvesting. A gradient-based optimization approach was carried out to maximize the absorption of infrared (IR) radiation around 10 µm. Owing to the near-field coupling of resonators with optimal design parameters, the peaks of the absorption responses approach each other, thus broadening the overall bandwidth with almost unity absorptivity. The proposed design has a resonance at 10 µm resulting from magnetic polaritons (MPs) and thus maintains high absorption above 99% up to a range of incident-angles greater than 60° and exhibits a polarization-free behavior due to symmetry. When the optimal design was numerically examined to fabrication tolerances, it showed negligible sensitivities in the absorptivity with respect to design parameters. The strong electric field enhancement inside the split-ring gaps and between the ends of the cross arms and the surrounding ring enables designing MIM diodes to rectify the harvested thermal radiations at 288 K. MIM diodes can be built by the deposition of thin insulators to sit in these gaps. The MIM diode and MPA work together to harvest and rectify the incident IR radiation in a manner similar to the operation of rectennas. The MPA outperforms the traditional nano-antennas in impedance matching efficiency because of its higher resistance. Also, its dual-polarization reception capability doubles the rectenna efficiency. Our proposed MPA retained absorptivity more than 99% when coupled with MIM diodes whose resistances are in the range of 500 Ω-1 MΩ.