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This paper reports the investigation of strains in waveguides fabricated on 5 mol% MgO-doped lithium niobate with different crystallographic orientations by proton-exchange process in pure benzoic acid using double-crystal x-ray symmetric and asymmetric diffraction method. Three-dimensional strains with high degree of anisotropy and constant values are revealed in proton-exchanged MgO:LiNbO3 waveguides for the first time. The strain relaxation observed in the experiment may be helpful to understand the instabilities of mode effective refractive indices. The less value of vertical strain measured on Y-cut MgO:LiNbO3 waveguides compared with that on Y-cut waveguides made of undoped LiNbO3 may explain the no surface damage of the former when pure benzoic acid is used as proton sources.

An experimental study has been carried out on the active control of surge in a centrifugal compression system. With a computerized on-line control scheme, the surge phenomenon is suppressed and the stable operating range of the system is extended. In order to design the active control scheme and choose the desired parameters of the control system inputs, special emphases have been placed on the development of surge inception and the nonlinear interaction between the system and the actuator. By use of the method designed in the present work, the results of active control onsurge have been demonstrated for the different B parameters, different prescribed criteria and different control frequencies.