30W, 1178nm Yb-doped Photonic Bandgap Fiber Amplifier

High power ytterbium fiber lasers at extremely long wavelengths by photonic bandgap fiber technology

“…ASE suppression in the high-gain region [39,40], lasing in a 1080-1140 nm region [39] and at 1178 nm [41], and highpower, high-efficiency fiber amplifiers in a 1150-1200 nm region [16][17][18][19][20] have been reported. But it should be noted that high-efficiency operation in this spectral region is really challenging.…”

“…7) are not sharp enough to suppress the gain growth at the wavelengths shorter than 1178 nm. Therefore, we coiled the fiber to smaller diameters to fine-tune the short-wavelength cut-off and steepen the loss slope [16][17][18][19][20]. The fibers coiled with D = 26 cm, the optimal coiling diameter determined experimentally, have loss slopes steeper than the gain and can be free from ASE in the wide spectral region.…”

“…However, since the high gain in a 1030-1100 nm region creates strong amplified spontaneous emission (ASE) and can lead to parasitic lasing, high-power long-wavelength Yb fiber laser/amplifier has also been challenging. We have been investigating Yb-doped solid-core photonic bandgap fiber (PBGF) for that breakthrough enabling ASE-free power scalable operation: the Yb gain profile is engineered by forming the low-loss photonic bandgap transmission window around the signal wavelength, whilst the undesired gain at <1140 nm is perfectly eliminated by sharp-cut distributed filtering outside the bandgap [16][17][18]. Recently we have achieved a stateof-art fiber amplifier with a 167 W output power, 61% slope efficiency, and 15 dB saturated gain at 1178 nm [19,20].…”

Power-scalable long-wavelength Yb-doped photonic bandgap fiber sources

“…One fiber (PBG-2008-10.1) has a pitch of 10.1 µm and is identical to the one used in [18][19], while the additional three fibers were newly fabricated. The new fibers (PBG-2009-10.1, PBG-2009-10.2, and PBG-2009-10.3) have cladding pitches of 10.1, 10.2 and 10.3 µm respectively.…”

“…7 is similar to the setup used in [18,19]. An unpolarized fiber Raman laser (FRL) at 1178 nm was used as seed source and the amplifier was seeded with ~5 W, well above the saturation power level in order to ensure gain saturation.…”