Abstract: A demultiplexer-free wavelength division multiplexing receiver based on cascaded-bandgap waveguide photodiodes, includes a substrate; and a plurality of different absorbing material sections forming a plurality of independent photodetector sections, each with a different thickness and a different bandgap. The plurality of photodetector sections may be fabricated at the same time on the same substrate, whereby different widths between each pair of mask stripes results in a different thickness of each photodetector section and a different bandgap of each photodetector section. The photodetector sections are then optically connected together into concatenated photodetector sections forming a single elongated optical waveguide.