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A figure-8 laser is a fiber laser with a figure 8-shaped ring resonator. It is used for making pico- and femtosecond soliton pulses. The typical spectrum of such a laser consists of a wide central peak and a few narrow lateral peaks that are placed symmetrically around it. The amplitudes of the narrow peaks are the same as or less than that of the central peak.
Both loops of the resonator work as Sagnac loops. The active medium of the laser is optical fiber with its core doped with rare earth ions. It is placed asymmetrically with respect to the resonator loops to make a nonlinear difference in phase between opposite waves, ensuring mode locking. In 1992 a figure-8 laser was built which had a smaller loop length of 1.6 m and a larger loop length of 60.8 m for generation of 315 fs pulses with interval 125 MHz.