Extended Regular Expressions of Star Degree at Most Two. - Kosaburo Hashiguchi; H. Yoo (Theor. Comput. Sci., 1990)

Extended Automata-Like Regular Expressions of Star Degree At Most (2, 1). - H. Yoo; Kosaburo Hashiguchi (Theor. Comput. Sci., 1991)

External Optical Modulator Using a Low-Cost Fabry-Perot Laser Diode for Optical Access Networks. - H. J. Lee; H. Yoo; Yong-Deok Jeong; Yong-Hyub Won (OpNeTec, 2004)