Nonlinear Fiber Optics - 4 ed. Agrawal

9.5. Brillouin Fiber Lasers 359
Figure 9.19: Schematic of a Brillouin fiber laser with two fiber loops containing optical circulators
(cir2 and cir3) and acting as two mirrors of a Fabry–Perot cavity. WSC stands for a
wavelength-selective coupler. (After Ref. [146]; c○2005 OSA.)
60 nm was realized in a 2005 experiment [146]. Figure 9.19 shows the cavity design
schematically for this laser. Two fiber loops act as mirrors because of the embedded
optical circulators. The SBS gain is provided by 8.8 km of single-mode fiber (SMF-28),
pumped with an external-cavity semiconductor laser tunable from 1520 to 1620 nm.
The 10-m-long EDFA is pumped at 980 nm using another semiconductor laser. The
tuning range and the number of Stokes line produced by such a laser varied with the
relative power levels of two pump lasers.
In an interesting configuration, the SBS pump is generated internally through selfseeding,
and only one laser is needed for pumping the EDFA [145]. Figure 9.20 shows
the laser design schematically. The ring cavity contains a 16-m-long EDFA and 5-km
of standard fiber to produce SBS gain. A Sagnac loop, built using a polarizationmaintaining
fiber (PMF), is used as a mirror. This mirror doubles the SBS gain as light
passes through the 5-km fiber twice during each round trip. The Brillouin pump is first
Figure 9.20: Schematic of a self-seeded Brillouin fiber laser: OC, PC, PMF, and OSA stand for
optical circulator, polarization controller, polarization-maintaining fiber, and optical spectrum
analyzer, respectively. (After Ref. [145]; c○2005 OSA.)