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Efficient waveguide-type four-color (red–green–blue–infrared) laser beam combiner for compact laser beam scanning image projectors

Abstract

A waveguide-based combiner that can combine an infrared laser beam with primary color (red, green, and blue) laser beams is proposed and analyzed using a simulation based on the beam propagation method. The combiner comprises four single-mode waveguides for individual light inputs and four directional couplers to change the light transmission path. Introducing the characteristic symmetrical arrangement of these waveguides and couplers results in an excellent performance for the four-color (red–green–blue–infrared) waveguide-based combiner. The symmetrical arrangement essentially reduces the combiner size without degrading the combining efficiency even though an additional combining color is added. The total length of the combiner is only 2.5 mm, in spite of the fact that the simulated combining efficiency averaged over the red, green, blue, and infrared colors is as high as 94%. In addition, a combining efficiency of more than 80% is obtained over a wide wavelength region of 35 nm. The effect of the polarization difference on the combining efficiency is negligible, i.e., almost within ± 1%. The analysis of the combining efficiency dependence on the gap width of the directional coupler composing the combiner indicates a large fabrication tolerance for process condition fluctuations. The proposed four-color (red–green–blue–infrared) combiner is expected to expand the functionality of compact laser beam scanner-based displays.

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Acknowledgements

The authors would like to thank S. Yonezawa, H. Kosugi, H. Higuchi, Y. Kitade, N. Okuno, H. Yoshimoto, K. Tokuda, and Y. Hirose from University of Fukui, and M. Kawasaki, Y. Kamei, K. Horii, A. Himeno, O. Kawasaki, K. Iwabata, and Y. Yabe from SEIREN KST Corp. for their valuable discussion and continuous support.

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Correspondence to Akira Nakao.

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Nakao, A., Yamada, S. & Katsuyama, T. Efficient waveguide-type four-color (red–green–blue–infrared) laser beam combiner for compact laser beam scanning image projectors. Opt Rev 29, 298–304 (2022). https://doi.org/10.1007/s10043-022-00743-2

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  • DOI: https://doi.org/10.1007/s10043-022-00743-2

Keywords

  • Laser beam combiner
  • Optical waveguide
  • Directional coupler
  • Laser scanning image projector
  • Infrared laser beam
  • Near-eye display