High-efficiency multiple-light-source red-green-blue power combiner with optical waveguide mode coupling technique

摘要

We propose a very low loss multiple-light-source red-green-blue (RGB) power combiner by optical waveguide mode coupling technique. The combiner consists of a two-step circuit that performs both power coupling and wavelength multiplexing for an RBG multiple-light source. The first step of the circuit combines first R, G, and B as the Oth-order mode. The second step combines second R and G by mode conversion from the Oth-order mode to second-order modes using waveguide mode couplers. We used an even mode configuration to avoid asymmetric deformation of the beam due to interference between the modes. By using all of these coupler functions in the two steps, the circuit provides multiple-light-source (RRGGB) power combining. The combiner was fabricated by silica planar lightwave circuit (PLC) technology. The coupler length is about 4.5 mm, including 2.3 mm for the Oth-order coupler and 2 mm for the second-order coupler. We estimated the coupling loss of both the Oth-order RGB coupler and second-order RG power coupler to be about 1 dB by evaluating the combined power for the Oth-order RGB couplers and the complementary output powers for mode couplers. To the best of our knowledge, this is the first demonstration of a multiple-light-source RRGGB power combiner using multimode coupling. This method enables us to combine a much larger number of light sources using multi-stage coupling for different modes as well. Moreover, the beam shape can be controlled by mode selection.