Liquid Crystal Based Electro-Optic Bragg Gratings for Laser Beam Attenuations

This paper provides research progress in the development of fast electro-optic gratings based on liquid crystals for laser beam attenuations. The electro-optic phase grating is formed by the phase separation of similar to 100nm liquid crystals droplets from a polymerizing organic matrix using holographic interference technique. The formed grating separates the incident laser beam into the output beams: the transmitted and diffracted beam, whose intensities can be electrically adjusted through electro-optic effect. The fast electro-optic gratings have a very fast electro-optic response time of 50 microseconds with diffraction efficiency above 99.8%. Optical receivers used in FSO have a limited dynamic range and there is a need for in-line variable attenuators to keep the signal levels from overloading the receiver. These attenuators should be continuous, provide sufficient attenuation, and also provide a low insertion loss for weak signal reception. The use of electro-optic Bragg gratings is one solution to, meet the requirements for an in-line attenuator for FSO.