Hoon JEONG^*, Hyoyeong PARK, Seungtaek KIM, Jongseok KIM, Chulsoo BYUN, and Cheolho KIM

Manufacturing System Division, Korea Institute of Industrial Technology, Cheonam, Chungnam 331-825, Republic of Korea

(Received December 7, 2011; Accepted January 13, 2012)

Master oscillator power amplifier (MOPA) technology has been widely used in high-power or ultrashort-pulse fiber laser systems because the shape of the laser pulse can be easily adjusted. Usually, the first amplification stage of a 1064 nm fiber laser uses the core-pumped Yb-doped fiber amplifier (YDFA); however, the gain or output power is limited owing to the strong amplifier spontaneous emission (ASE) in the 1030 nm band. This paper presents the improved output power in an YDFA by inserting an additional unpumped Yb-doped fiber, which absorbs the lost backward ASE emitted from the pump end. We achieved an output power increase of more than 10% in a low-power signal, and the increase in output power decreased as the signal power increased. Moreover, the insertion of an additional unpumped Yb-doped fiber restricted the unwanted 1030 nm lasing in a low-power signal.

Key words: fiber laser, master oscillator power amplifier, unpumed Yb, backward spontaneous emission, core pumping

^*E-mail address: hoonj@kitech.re.kr