A large-area, waveguide-based, high-speed ultraviolet and visible light photodetector system for optical wireless communication includes a substrate; plural, parallel, waveguides formed directly on the substrate and including a high quantum-yield wavelength-converting material of semiconductor nature; an optical coupling system optically connected to each one of the plural, parallel, waveguides; and a photodetector optically connected to the optical coupling system and configured to detect an outgoing light. The wavelength-converting material converts a first wavelength of an incoming light at high-speed, received by the plural, parallel, waveguides, into a second wavelength of the outgoing light. The first wavelength is different from the second wavelength, and the first and second wavelengths are between 200 and 800 nm.