Invisible grid-pattern structure light has often been used for being shined on objects for contour reconstruction based on
the distortion of grid pattern, for vehicle collision prevention etc. However, the structure light can be easily disturbed by
surrounding nature light even if infra-red (IR) light source is used because natural light contains quite an amount of IR
spectrum. In this paper, it is proposed that the structure light is provided from a highly coherent laser source, so that the
structure light pattern reflected from the target object will contain not only the distorted irradiance distribution of grid
pattern, but also laser speckle associated with it. The laser speckle pattern depends on the surface roughness of the target
object, which provides extra information for extracting the distorted grid pattern from the background irradiance of
surrounding natural light. The laser speckle pattern therefore helps to improve the immunity for surrounding light
disturbance, and hence the robustness and reliability of contour reconstruction system. A binary surface relief phase-type
diffractive optical element(DOE) has been proposed for generating desired pattern directly at far field when working
together with laser light source. The design process is based on iterative Fourier transform algorithm(IFTA) in scalar
diffraction theory.
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