Abstract. In this work a study of the characteristics of the
output radiation of a Raman fiber amplifier at a wavelength of 1650 nm when
comparing direct and reverse pumping performed at a wavelength of 1540 nm was
carried out. The amplifier is designed for lidar measurements of methane
concentration in the Earth's atmosphere. A model calculation of the output
power was used on the basis of exact equations for the propagation of pumping
in the fiber in the forward and backward directions. Also we made a direct
experiment comparing both pump types with a power of 3.5 W in a fiber with a
length of 1500 m. The study showed the advantage of reverse pumping in Raman
amplifiers in the wavelength range of ~ 1650 nm both in terms of output power,
as well as in spectral purity of the output signal, which is especially valuable
for lidar applications. A qualitative explanation of this effect consists in a
more efficient use of pumping: with small input signals, together with low
pumping at the initial length of the active fiber and at high pumping, together
with a large signal on a finite length of fiber. The filtration of the pumping
residuals is also better in this case. When the pumping is propagated back with
a small input signal, the noise characteristics of the output signal are
better, the spectrum is cleaner, the filtration of the pumping remains is
better. With large input signals, the difference in output power for both types
of pumping decreases: if for small signals this difference is 2-3 times, then
for large signals ~ 1.5 times. This is also understandable, since large input
signals with direct pumping efficiently remove the inversion on the initial portion
of the fiber, that is, the pumping is used more fully.
Keywords:
lidar, Raman amplifier, laser,
pumping
References
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For citation:
V. I. Grigorievsky.
Mathematical simulation and experimental comparison of
direct and reverse pumping in a Raman amplifier for lidar applications.
Zhurnal Radioelektroniki - Journal of
Radio Electronics. 2018. No. 8. Available at
http://jre.cplire.ru/jre/aug18/12/text.pdf
DOI
10.30898/1684-1719.2018.8.12