1.75-Kilowatt continuous-wave output fiber laser using homemade ytterbium-doped large-core fiber

Abstract

À3.43 dB) and À3.43 dB (À3.2 dB), respectively. The maximum value of amplitude unbalance, the difference in power of S 31 and S 21 between two output ports, is measured (simulated) at 0.7 dB (0.35 dB) in the operating band. Figure 7 shows the simulated and measured phase differences between two output ports. The simulated phase differences between two output ports of a conventional MSL Wilkinson balun are compared. The conventional MSL Wilkinson balun are designed using two branches of À90 and À270 phase shift MSL. The differential output phase is shown to be flat in the operation band of the proposed balun. The fractional 180 6 10 bandwidth of the balun based on the PLH TL is measured (simulated) at 71% (70%) from 1.47 GHz (1.44 GHz) to 3.09 GHz (2.99 GHz), whereas the bandwidth of the conventional MSL balun is only 10.8% from 2.36 GHz to 2.63 GHz. Consequently, the broadband Wilkinson balun based on a PLH TL has good properties, such as return loss, isolation, and through in the broad frequency range.Furthermore, a wideband balun based on modified PLH TL [6] having a wide LH bandwidth is designed by the full wave simulation. The illustration of Figure 7 shows the top view of the modified PLH TL. The other dimensions of modified PLH TL are exactly the same with those of Figure 1 except for dimensions in figure caption of Figure 7. In this case, to satisfy the Eq. (4), the lengths of L 1 and L 2 are determined as 20.8 mm (corresponding to 4-stage modified PLH TL) and 60.3 mm, respectively. The designed balun has the fractional bandwidth of 107.8% from 1.12GHz to 3.74GHz, as shown in Figure 7. Consequently, the PLH TL balun is well-suited for RF devices requiring a broadband balanced signal. CONCLUSIONS ABSTRACT:We have demonstrated a homemade high-efficient ytterbium-doped fiber laser with up to 1.75 kW of continuous-wave output power at 1.09 lm with a slope efficiency of 76%. The fiber is pumped by two laser diode array (LDA) sources launched through opposite ends. No undesirable effect is observed with increasing pump power, which suggests that the homemade fiber laser could produce higher power output by using more pump sources.

First experimental investigation of the amplification of a Yb-doped fiber laser pumped with 1000 and 1014-nm laser diodes

“…According to Eq. (1), the quantum defect using new wavelengths for pumping is lower than that of the conventional wavelength (*975 nm) [7,8] used in direct pumping, which promises an improved amplification efficiency. The absorption and emission cross sections of Yb ion [12] in silica (that is used as the main fiber of amplifier in our experiment) are plotted in Fig.…”

“…However, the power of YDFLs has been limited to the kilowatt level mainly because of the low brightness of the pump source and the high thermal load inside the fiber [5,6]. In the classical structure, direct pumping at 975 nm is usually employed to scale the laser to a higher power [7,8]. Recently, another pump scheme called tandem pumping has been used as an effective way of scaling the power beyond the kilowatt level [9].…”

Heat Generation and Removal in Fiber Lasers

“…Due to eminent efficiency, good compactness and reliability, outstanding spatial beam quality, efficient heat dissipation, and freedom from thermal lensing, fiber lasers are now competing with their bulk solid-state counterparts for interesting scientific and industrial applications [1][2][3] such as material processing, defense, remote sensing, free-space communication, etc. With the availability of high-power and high-brightness laser diodes accompanied with cladding pumped architecture, a rise in output power from ytterbium (Yb)-doped, double-clad fiber laser sources has been dramatic recently, maturing to the point of hundreds of Watts [4][5][6], even in the case of continuous-wave (CW) regimes, 10/50 kW for single-transverse-mode/ multi-mode operations [7], and beyond.…”

Optical properties of high power S-band fiber oscillators and amplifiers

“…In recent years, YDFLs have developed very fast and the output power has been scaled to several kilowatts in the continuous-wave regime [1][2][3][4][5][6] . However, further power scaling is hindered by thermal, nonlinear, pumping, and damage-related problems [7,8] .…”