An on‐chip quantum light source based on spontaneous four‐wave mixing is an essential element for developing quantum photonic integrated circuit technology, which has the advantage of no connection loss owing to the integration of the source into photonic circuits. The waveguide‐based quantum light source inevitably causes propagation loss owing to imperfections in the fabrication process, but the propagation loss effects on photon‐pair generation have not been extensively studied. In this study, propagation loss effects were examined using theoretical and experimental methods. In theory, the performance of quantum light sources, such as brightness, heralding efficiency, and coincidence‐to‐accidental ratio, strongly depend on propagation loss. We fabricate several waveguides with a moderate propagation loss of 2.2 dB/cm to investigate the loss dependence and ascertain that the brightness, heralding efficiency, and coincidence‐to‐accident ratio strongly correlate with the length of the optical waveguide. The maximum coincidence‐count brightness occurred at an optimization length of 1/ α , where α is the absorption coefficient. In contrast, the single‐count brightness shows slightly different waveguide length dependence owing to loss‐induced one‐photon states. We expect that the results obtained in this study will greatly assist in determining the proper waveguide length for photon‐pair generation according to the source’s application fields. The results will be helpful in the development of a quantum light source suitable for practical and quantum optical integrated circuits and will lead to the development of high‐fidelity quantum technologies.

An on-chip optical power splitter is a key component of photonic signal processing and quantum integrated circuits and requires compactness, wideband, low insertion loss, and variable splitting ratio. However, designing an on-chip splitter with both customizable splitting ratio and wavelength independence is a big challenge. Here, we propose a tailorable and broadband optical power splitter over 100 nm with low insertion loss less than 0.3%, as well as a compact footprint, based on 1×2 interleaved tapered waveguides. The proposed scheme can design the output power ratio of transverse electric modes, lithographically, and a selection equation of a power splitting ratio is extracted to obtain the desired power ratio. Our splitter scheme is close to an impeccable on-chip optical power splitter for classical and quantum integrated photonic circuits.