Contents I. Introduction
The photodetector is a key component for a variety of applications ranging from optical communication to quantum cryptography and THz photonics. Besides the existing technologies that are constantly progressing, novel devices and materials have been also introduced to achieve ultra-fast, ultra-sensitive and ultra-low-noise photodetection. In particular, superconducting optoelectronics have received much attention recently [1]–[9]. This is, in part, due to the intrinsic characteristics of superconductors that offer very high sensitivity to optical illumination, ultra-low-noise operation at cryogenic temperatures and ultra-fast photoresponse [8]–[16]. Moreover, recent developments in fabrication techniques have opened new routes to integrate superconducting structures with photonic elements such as optical waveguides and cavities [17]–[19].
