1. Danh. Commercial laser lines. https://commons.wikimedia.org/wiki/File:Commercial_laser_lines.svg.
2. The Creative Commons copyright licenses. https://creativecommons.org/licenses/.
3. Winkler H, Vinh QT, Khanh TQ, Benker A, Bois C, Petry R, et al. LED components – principles of radiation generation and packaging. In: LED lighting. Weinheim: Wiley; 2014. p. 49–132.
4. Mrzeon. Optical fiber types. https://commons.wikimedia.org/wiki/File:Optical_fiber_types.svg.
5. SKS S. aP. Review on optical waveguides. In: You KY, editor. Emerging waveguide technology. Rijeka: IntechOpen; 2018.