FIBER PHASE CONJUGATORS AT 1064-NM, 532-NM, AND 355-NM WAVELENGTHS

Undoped multimode quartz fibers can be used as effective phase conjuga tors with high fidelity and reflectivity for improving the beam qualit y of lasers with high average power. Such phase conjugators based on s timulated Brillouin scattering (SBS) in undoped multimode quartz fiber s with a core diameter of 100 mu m and a length of more than 2 m were characterized at wavelengths of 1064, 532, and 355 nm. The power thres holds 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, witho ut a significant depolarization owing to the fiber. Direct measurement of the far-field fidelity, i.e., the phase-conjugated part of the ref lected light in the far field at 1064 nm, results in a fidelity of mor e than 90%. (C) 1997 Optical Society of America.