Abstract

A dynamic hologram can always be updated to allow for any movement of the optical components (like the drift in the alignment of the optical component over time). This makes the dynamic hologram very useful in optical signal processing. We have studied the diffraction efficiency that can be obtained from dynamic photorefractive gratings as a function of the intensity of the read beam and the direction of readout. For small two-beam coupling constants, the diffraction efficiency is independent of the intensity of the read beam as long as it is weaker than or equal to the intensity of the write beams. For large two-beam coupling constants, there seems to be an optimum value of the intensity of the read beam for which large diffraction will occur, after which it eventually falls to zero with increasing read beam intensity due to erasure of the grating being read. The maximum value of the diffraction efficiency of the read beam can be 50% or 100%, depending on the sign of the two-beam coupling constant. This change of sign corresponds to readout from the two different input ports for equal intensities of the write beams and demonstrates the nonreciprocal nature of the photorefractive gratings—a diffraction efficiency that is dependent on which input port the photorefractive grating is being read from. This is because from one readout direction, the grating written by the read beam and its diffracted beam reinforces the grating being read, thus leading to high diffraction efficiencies. Readout from the other direction results in the two gratings being out of phase, leading to a lower diffraction efficiency in this case.

© 1989 Optical Society of America