Self-switching fiber loops imbalance by fiber dispersion

Abstract

Using stimulated Brillouin scattering (SBS) in glass fibers as phase-conjugating process, the field of application of SBS phase conjugators' can be expanded, because fibers offer a lowpower threshold and a stable performance even at high input energies in contrast to liquid and gas SBS phase conjugators. Undoped multimode quartz fibers with a core diameter of 200 pm were tested as phase conjugators with high fidelity and reflectivity for 1064-nm wavelength in Ref. 2. Only the first two meters of a fiber contribute constructively to the stimulated Brillouin scattering process for input pulses with a coherence length of about 50 cm, so that attenuation in the fiber plays only a secondary role. Therefore, fibers with higher attenuation at shorter wavelengths can be still used as phase conjugators. We present results of fiber phase conjugators at three wavelengths from near-infrared 1.06 pm over visible 532 nm to nearultraviolet 355 nm. The SBS threshold, reflectivity and fidelity were characterized. Commercial all-silica multimode quartz glass fibers with a step-index structure, a core diameter of 100 pm and a cladding diameter of 110 pm were used. The core is made from undoped quartz glass. The numerical aperture NA is 0.22, which corresponds to a maximum full angle of 25.4' (-440 mrad) for coupling light into the fiber. The lengths of all investigated fibers were more than 2 m. The attenuation of the used fibers is about 2 dB/km at 1064 nm, 30 dB/km at 532 nm and 45 dB/km at 355 nm. At a fiber length of 2 meters, losses of about 0.2% at 1064 nm, 3% at 532 nm and 4% at 355 nm are expected for a pulse traveling forth and back the fiber. Figure 1 shows the experimental setup for our investigations. A NdYAG oscillator-