Improvement of Output Characteristics of a Large-Mode-Area Er-Doped Fiber Amplifier Pulse Pumped by a Cascaded Raman Fiber Laser With a Low Repetition Frequency

Abstract

We improve the output of a MOPA system that emits single-frequency high-energy optical pulses using a large mode area Er-doped fiber amplifier pumped by a cascaded Raman fiber laser with a low 150 Hz repetition frequency. It is found that the unwanted light generated in the cascaded Raman fiber laser at the same time as the pump light saps the gain of the amplifier and degrades its output characteristics. By combining the removal of unwanted light with a pulse pump technique, the pulse energy is improved from less than 1.0 mJ to 1.2 mJ with at the same time a SNR of 30 dB compared to 19 dB before the improvement. The percentage of power in the signal also improves from 61.0% to over 90.7%.

Single-frequency high-energy pulses from an Er:Yb glass planar waveguide amplifier with good beam quality

“…6) In particular, pulses with a high energy (>1 mJ), a long pulse duration (>100 ns), a single frequency and good beam quality (M 2 < 2) are required in the research field of coherent Doppler wind lidars (CDWLs). [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Several groups have developed master oscillator power amplifier (MOPA) systems using an Er, Yb: co-doped fiber amplifier [10][11][12][13][14][15][16] or an Erdoped fiber amplifier (EDFA) [17][18][19][20][21][22][23] with a large mode area (LMA) to avoid stimulated Brillouin scattering (SBS) and laser induced damage (LID). Most work on all-fiber MOPA systems has been demonstrated with pulse energies of up to 1.5 mJ due to SBS or amplified spontaneous emission (ASE) dynamics.…”

“…[25][26][27] A symmetrical double under-cladding structure with a 50 μm core was employed to increase the volume of the PWA's active area and to mitigate the possibility of LID. An LMA EDFA 20,23) was introduced to increase the energy of the input pulses significantly over that of a single-mode EDFA. In this case, limiting of the energy and degradation of the SNR to 18 dB were observed due to parasitic oscillations in the large PWA when using high density pumping.…”

“…The pump beams propagate in the double clad waveguide on a single pass. Since we have already had knowledge of the effect of the pump pulse width on the output ASE characteristics of amplifiers, 23) we maintain all the pulse pump widths at 1.0 ms when the f rep is changed. The total maximum pumping energy for the PWA is 289 mJ.…”