OBSERVATION AND COMPENSATION OF FREQUENCY DETUNING IN HIGH-REFLECTIVITY BRILLOUIN ENHANCED 4-WAVE-MIXING

Details of the frequency relationships among interacting beams in Brillouin enhanced four-wave mixing (BEFWM) are examined. A new technique using two individually injection-seeded single-mode lasers allows for precise control and knowledge of the relative wavelengths of the interacting beams. This is compared with the standard frequency-shifting technique employing a single laser in conjunction with stimulated Brillouin scattering (SBS) frequency shifters. A continuously tunable frequency difference ranging over many gigahertz is achieved, resulting in a valuable tool for the investigation of nondegenerate four-wave mixing processes such as BEFWM. Two variations of BEFWM are studied: omega-pump1 - omega-pump2 = 0 with noncollinear pumps; and omega-pump1 - omega-pump2 = omega-SBS with collinear pumping. Resonance spectra of BEFWM gain versus probe-pump frequency shift show a significant detuning in the frequency for the gain maximum from the expected Brillouin shift for the former case. When the probe-pump frequency is tuned in compensation for this detuning, improvements in BEFWM phase conjugation are realized in comparison with more conventional techniques using SBS frequency shifting.