GB1313591A - Acousto-optic devices - Google Patents

Abstract

1313591 Modulating light CHROMATIX Inc 23 April 1970 [1 May 1969] 19497/70 Heading H4F When the k-vectors of an acoustic wave and a plane polarized optical beam passing through an anisotropic medium are collinear, the optical beam will undergo a type of Bragg diffraction which is cumulative in effect only for a narrow band of optical frequencies and non-cumulative by self cancellation for other frequencies. The diffracted narrow waveband portion of the beam is collinear with the undiffracted remainder of the beam but is plane polarized orthogonally thereto, so that by using an output analyser, and by varying the acoustic frequency and thus the wavelength of the diffracted portion, a variable optical filter can be made. Thus in Fig. 1, polarized light 13 enters a LiNbO 3 crystal 12 at the Brewster angle, and a transducer 16 supplies a variable frequency longitudinal acoustic wave to the crystal, which is converted to a shear wave 24 collinear with the optical beam on reflection from a crystal face 21. The transmitted light 14 is analysed at 15. In Fig. 5 (not shown) incoming light is polarized by a Roden prism and enters a LiNbO 3 crystal with end faces normal to the optic axis. The beam is reflected from the remote end face of the crystal, to which the acoustic transducer is attached and the Roden prism deflects the diffracted narrow waveband portion of the reflected beam away from the main optic axis. Other useful materials for the crystal 12 are sapphire and quartz. It is stated that the condition for diffraction in such systems is: k e +k a =k o where k is the momentum vector and the subscripts e, o and a refer to the input extra-ordinary, output ordinary optical beams, and the acoustic wave respectively.