We propose a new simple structure-based color combiner with red, green, and blue (RGB) laser diodes (LDs) and a thermally expanded core (TEC) fiber waveguide. As the color combiner used the LDs as optical sources, the total volume of the color combiner could be minimized as 3.84 cc and the output powers of RGB optical sources in the color combiner could be obtained efficiently as 10.324, 13.290, and 10.150 mW, respectively. A TEC fiber waveguide was used as a medium for color combination of RGB in the color combiner. As the TEC fiber waveguide was used as a key component for color combination, we could observe the color combiner had the degree of uniformity and the matching accuracy was good. The measured degree of uniformity and matching accuracy of RGB beams were 121 µm (in large diameter), 56 µm (in small diameter), and 109 µm (on x-axis), 20 µm (on y-axis), respectively.