Optical Switching and Control Techniques Using Nonlinear Optical Wave Mixing

摘要

We show experimentally that thermooptically induced beam guides and phase grating structures can be used to efficiently switch an optical beam by redirecting its energy in times of 20 and 2 nsec, respectively. Beam guiding was achieved by passing a focused, TEM at infinity laser pulse through an absorbing liquid to which an absorbing dye had been added. Heating of the liquid in the focal region by the Gaussian profile beam changed the refractive index to produce a long cylindrical volume analogous to a graded-index (GRIN) optical fiber. Radiation from a second laser beam not absorbed by the liquid could be coupled into the graded index real-time fiber and redirected by it with in efficiency as high as 90%. The switch-on time was measured to be 20 nsec and persisted without intervention for about 1 millisecond (i.e. optical memory). The rise and decay times are in good agreement with calculations using a simple thermal model which describes the process. The thermo-optically induced phase grating was generated by interfering two beams of laser radiation in an absorbing liquid. Heating of the liquid along the interference pattern produced a sinusoidally varying refractive index pattern or phase grating. This real-time optically generated grating was used to switch (redirect by diffraction) a probing laser beam. For a small crossing angle of 7 deg, a switching time of 2 nsec was measured and was in good agreement with the thermal model, as was the measured diffraction efficiency of 15%.