Diffractive, polarization modulating optical devices

An optical device operative to apply a diffractive effect to produce a diffracted first image and a phase modulation-retardation to produce a polarized second image, said device comprising:

• an encoding surface having a micro-relief pattern (22) carried over at least part thereof and having a grating direction,
• the micro-relief grating having a predetermined spatial distribution in which the orientation of the grating direction varies across at least part of the encoding surface thereby to produce a predetermined diffracted first image when illuminated in use, and
• a solid optically anisotropic layer (26) formed of a polymerized liquid crystal material operative to produce a phase modulation-retardation polarized second image, the local optical axes of the polymerized liquid crystal material lying substantially parallel to said encoding surface, and each axis being in respective alignment with the local grating direction of a corresponding adjacent part of the micro-relief grating so that the orientation of the local optical axes of the polymerized liquid crystal material of said optically anisotropic layer (26) varies across the encoding surface,
• wherein said optically anisotropic layer (26) imposes a predetermined spatial distribution of polarization modulation to produce a predetermined polarized second image when illuminated in use, so that both a diffracted image and a polarized image are produced in which both the diffracted image and the polarized image vary spatially across at least part of the overall image.