Fiber phase conjugators at 1064-nm, 532-nm, and 355-nm wavelengths

Undoped multimode quartz fibers can be used as effective phase conjugators with high fidelity and reflectivity for improving the beam quality of lasers with high average power. Such phase conjugators based on stimulated Brillouin scattering (SBS) in undoped multimode quartz fibers with a core diameter of 100 $\mathit{\mu }\mathrm{m}$ and a length of more than 2 m were characterized at wavelengths of 1064, 532, and 355 nm. The power thresholds at these three wavelengths are 6.4, 3.3, and 3 kW, respectively, and the maximum SBS reflectivity is more than 50% in all cases, without a significant depolarization owing to the fiber. Direct measurement of the far-field fidelity, i.e., the phase-conjugated part of the reflected light in the far field at 1064 nm, results in a fidelity of more than 90%.