Efficient High Power ns Pulsed Fiber Laser for Lidar and Laser Communications
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1076-K01-04
Efficient High Power ns Pulsed Fiber Laser for Lidar and Laser Communications Jian Liu Fiber Laser Research, PolarOnyx, Inc., 470 Lakeside Drive, Suite F, Sunnyvale, CA, 94085 Abstract Research results on high energy/power ns pulsed fiber lasers are discussed in this paper. Modulation schemes for a seed laser in getting various optical waveforms, high power operation of fiber amplifiers, nonlinearity mitigation in high power fiber lasers, and trade-offs have been addressed. It shows experimentally that ns pulses can be achieved by direct modulation of a semiconductor seed laser and an energy level of submJ were demonstrated. 23 % wall plug efficiency was achieved for a compact laser module.
Introduction
Figure 1 High power fiber lasers is an enabling technology for NASA deep space communications and Lidar applications For future NASA’s deep space missions and Lidar applications, high energy pulsed fiber lasers have been considered to be an enabling technology to build high power transmitters [1-10]. The next generation pulsed fiber laser requires a weight of smaller than 1kg, high pulse repetition rate (> 10 MHz for communications and > 10 kHz for Lidars), ns pulse width, > 10 W average output power and > 1 kW peak power at 1.06 micron and 1.55 micron, and overall efficiency higher than 20%. In addition to those, high extinction ratio (>30 dB), high OSNR, and good pulse shape are highly desired for enhancing system performance to battle with attenuation, pulse distortion, and pulse delay towards longer distance of transmission [4-7]. These requirements eliminate classic Q-switch fiber lasers. Different amplification schemes can be used as alternatives to produce high energy and high repetition rate pulses via a gated amplification, and multiple isolated gain stages.
In this paper, various types of single frequency nanosecond fiber laser will be presented. Up to 20 W operation and sub-mJ fiber lasers were achieved with over 23% wall plug efficiency. Experimental Results on Pulse Shaping Fiber Laser Figure 2 plots the experimental setup for the demonstration of pulse shaping technology in the fiber laser. The checking points were labeled A through E in Figure 2. Both spectrum and pulse shape were taken at those checking points to evaluate the pulse evolution within the fiber laser. Pulse widths from 500 ns to 1 ns and repetition rates from 10 kHz to 60 MHz were obtained from our experiment by tuning the driving electronics of the seed laser. EDF I
975 nm
FBG
Laser
WDM C
B
A
D Pulse generator EDF II 975 nm pump
WDM E
Figure 2 Experimental setup for a pulse shaping fiber laser Figure 3 gives examples of Gaussian shape pulse generation and propagation in the fiber laser. The Gaussian shape pulse was generated by changing the driving current format and bias of the direct modulation DFB laser (the repetition rate can be tuned from 10 kHz to 60 MHz and the pulse width from 1 ns to 500 ns). Strong pulse shaping effects are shown in Figure 3 for Gaussian shape amplification at a repetition rate of 30
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