For quantum applications, it is important to generate quantum states of light and detect them with extremely high efficiency. For many future applications, it also important to do this at scale. This presents many engineering and metrology challenges. Further, as the technology matures, these single photon detectors and sources may also have new exotic applications in fields other than quantum optics. In the first half of this talk, I will discuss our efforts to develop a scalable silicon-compatible light sources and waveguide-integrated superconducting detectors. In the second half of the talk, I will discuss some of the open challenges and opportunities in metrology of single photon detectors, and our work on developing accurate absolute power calibrations at the single photon level.