Highly-efficient waveguide-type red–green–blue laser beam combiners for compact projection-type displays

Abstract

A waveguide-type RGB laser beam combiner was fabricated and its optical properties were measured and analyzed through comparison with a simulation. The combiner has three different waveguides for RGB light inputs, three directional couplers, and a single output waveguide. The fabricated combiner shows an excellent multiplexing efficiency of as high as 96.4%. The size of the multiplexing region of the fabricated combiner is as small as 2.3 mm. Furthermore, by optimizing the combiner structure, it was found that the multiplexing efficiency hardly depends on the gap width of the directional coupler in the combiner. The polarization dependence of the multiplexing efficiency was also measured. The difference in multiplexing efficiency between the TE and TM modes is within 4% when using the optimized combiner structure, demonstrating the small polarization dependence of the multiplexing efficiency. Thus, the fabricated combiner exhibit’s high performance, as well as excellent fabrication reproducibility, leading to the realization of compact laser scanning image projectors.