Abstract
We present a 2.2 GHz modulated, 1.27 kW output power, monolithic fiber amplifier based on pseudo-random binary sequence (PRBS) phase modulation. The spectral line spacing of maximizing the threshold enhancement factor (plateau of trend) was found by theoretical simulation. The spectral line spacing was adjusted to 12.7 MHz by a pattern length of n = 9, which is close to the plateau of trend in the proposed architecture. A 2.2 GHz low-pass radio frequency filter was used to control the FWHM of the seed. A four-stage Yb-doped fiber amplifier chain was established to boost a distributed Bragg reflector (DBR) laser and a distributed feedback (DFB) diode laser to 1.2 kW and 1.27 kW with a backward reflectively of <1‰, which shows a good suppression of SBS effect.
Highlights
We present a 2.2 GHz modulated, 1.27 kW output power, monolithic fiber amplifier based on pseudorandom binary sequence (PRBS) phase modulation
PRBS generates an spaced discrete optical power spectral density, and the spectral line spacing is a function of the modulation frequency and pattern length, which can make the spectral line spacing adjustment flexible[10]
Signal power of 1.27 kW and 1.2 kW were attained at distributed feedback (DFB) and distributed Bragg reflector (DBR) laser seeding with near diffraction-limited beam quality (M2 < 1.2), respectively
Summary
We present a 2.2 GHz modulated, 1.27 kW output power, monolithic fiber amplifier based on pseudorandom binary sequence (PRBS) phase modulation. Phase modulation techniques include driving the phase modulator with a sine wave[3], a flat-top spectrum radio frequency (RF) signal[4,5], or a white noise source (WNS)[6] etc Among these linewidth broadening methods, >20 GHz linewidth can be generally obtained. In the narrow linewidth fiber amplifier configuration, a proper spectral line spacing improves the SBS suppression for a given linewidth[11]. We applied PRBS phase modulation with a 2.2 GHz low-pass RF filter to control the longitudinal mode spacing of the single frequency master oscillator, aimed to equilibrate spectral homogenization and Brillouin gain-spectrum overlap in the narrow linewidth fiber amplifier. To the best of our knowledge, this is the highest power level for narrow linewidth fiber amplifier based on phase control under 5 GHz spectral linewidth
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