US Patent 11768342 Optical multiplexing circuit and optical source

In a conventional RGB coupler, the split ratio largely depends on the wavelength. The split ratio of R and the split ratios of G and B are non-uniform because R has a wavelength far from those of G and B. Accordingly, a video display device needs to have the monitoring detection value corrected, making it difficult to use the monitoring function. A light combining circuit and a light source of this disclosure include a first splitting unit for splitting R wavelength light and a second splitting unit for splitting G and B combined light. They split monochromatic light of R and combined light of G and B, independently. G and B light from an LD are first combined by a preliminary wave-combining unit before being split. The split lights of each wavelength are combined by a main wave-combining unit, outputting RGB combined light. Each split light from the two splitting units is detected by a single PD.