High-quality optical microcavities are prospective in many optoelectronics fields like optical communication, nonlinear optics, and quantum information technology. For quantum telecommunication over 1.55 μm silica-fiber-based networks, micropillar cavities containing quantum dots (QDs) are strongly required to construct quantum devices such as single-photon sources (SPSs). The straight way could be using micropillars composed of traditional InGaAsP/InP distributed Bragg reflectors (DBRs), which can in principle serve as efficient 1.55 μm SPSs. To reduce the difficulty in fabricating such ~30 μm high pillars, structure hybridizing semiconductor with dielectric materials is designed. Consisting of Si/SiO2 DBRs and an InP active layer, such a micropillar readily enhances the rate of single-photon emitting from an InAs/InP QD to be over GHz and serves as a photon-indistinguishable SPS. To strongly couple a 1.55 μm QD with an optical mode, the Si/SiO2-InP hybrid micropillar cavity can be reformed by introducing tapered DBR structures. This new hybrid pillar cavity can be diminished to have a sub-micrometer diameter, giving small mode volume and ensuring single QD emission. With quality (Q) factor as high as 105–106, this cavity can behave as a coherently controllable quantum device. More effective might be the InGaAsP/InP-air-aperture micropillar cavity, which can be fabricated by a monolithic process without hybridizing.
Part of the book: Optoelectronics
Focal-plane avalanche photodiodes (APDs) are being more and more widely and deeply studied to satisfy the requirement in weak light and single photon imaging. The progresses of this worldwide study, especially the distinctive researches and achievements in Southwest Institute of Technical Physics and University of Electronic Science and Technology of China are reviewed in this chapter. We successfully fabricated up to 64 × 1 linear-mode Si APD arrays, and 32 × 32–64 × 64 Si single-photon avalanche detector (SPAD) arrays, and applied them in Laser Detection and Ranging (LADAR) platforms like driverless vehicles. Also, we developed 32 × 32–64 × 64 InGaAsP/InP SPAD arrays, and constructed three-dimensional imaging LADAR using them. Together with the progresses of other groups and other materials, we see a prospective future for the development and application of focal-plane APDs.
Part of the book: Advances in Photodetectors