The majority of contemporary optical encryption techniques use coherent illumination
and suffer from speckle-noise pollution, which severely limits their
applicability even when information encoded into special “containers”
such as a QR code. Spatially incoherent encryption does not have this
drawback, but it suffers from reduced encryption strength due to
formation of an unobscured image right on top of the encrypted one by
undiffracted light from the encoding diffraction optical element (DOE)
in axial configuration. We present a new lensless encryption scheme,
experimentally implemented with two liquid crystal spatial light
modulators, that does not have this disadvantage because of a special
encoding DOE design, which forms desired light distribution in the
photosensor plane under spherically diverging illumination without a
converging lens. Results of optical experiments on encryption of QR
codes and successful information retrieval from decoded images are
presented. Conducted analysis of encryption strength demonstrates
sufficiently high key sensitivity and large enough key space to resist
any brute force attacks.