Compact multi-color laser combiner based on a scalable configuration of waveguide-type directional couplers

Compact multi-color waveguide-type combiners based on directional couplers (DCs) are presented. The essence of this combiner design concept is the introduction of through-type DCs in addition to normal DCs. In through-type DCs, only a small portion of the light propagating along one of the paired waveguides is transferred to another waveguide, while most of it propagates straight along the input waveguide. Introducing through-type DCs increases the flexibility of the combiner configuration, thus reducing the total combiner length and increasing the number of combined colors. Combining multiple colors, up to four, five, and even six, is also possible without degrading the combining efficiency. The fabricated blue-green-red-infrared four-color combiner reproduced the simulated design, verifying the scalability and applicability of the design concept to actual devices, such as laser displays or laser measurement systems, including laser scanning microscopes.