Scientists of the Institute of Laser and Plasma Technologies have proposed a scheme for optical encoding of information based on formation of the wave front and which works with spatially incoherent illumination. This scheme is effective in creating of highly secure, high-speed coding systems: the protection is provided by two-dimensionality of dynamically replaced coded keys. The study is published in the respected scientific journal "Laser Physics Letters".

Nowadays scientists from around the world are actively conducting research on the creation of optical encoding systems. The main direction of such studies is the development of advanced optical systems of information encoding with fully coherent laser illumination. Such studies are incompatible with usual photo- and video cameras, because they require the use of complex holographic methods and are focused on the elemental base of the next generation.

Experts consider the development of optical coding using spatially incoherent quasi-monochromatic (single color) illumination as a more effective approach. They provide a possibility of hardware implementation on the basis of photo and video cameras which are available commercially today.

The staff of MEPhI has implemented this approach. In this case information for encoding is displayed as a QR code on the LCD amplitude-spatial light modulator that is illuminated by monochromatic laser radiation. Radiation is passed through a rotating frosted diffuser, which destroys the spatial coherence. The researchers used a liquid-crystal phase light modulator as the encoding  element, where pre-synthesized diffraction optical elements are displayed. The camera's image sensor detects the optical convolution of the image that is output by the amplitude modulator with pulse response of the diffractive element, derived on the phase modulator.

The use of such modulators allows to change encoding keys in real-time. Decoding is performed by software-based method of digital deconvolution (inverse convolution in signal processing) with stabilization solution.

As a result of study, scientists successfully encoded and decoded the images of QR codes with a size up to 129×129 elements. The percentage of erroneously decoded pixels didn’t exceed 0.05%. It indicates a high ratio of "signal/noise" of the scheme: that is, its practical usage allows to avoid "graininess" of the image during recognition.

"The novelty of our work is, first, in the application of monochromatic spatially incoherent illumination of the encoding scene – it allows you to avoid the speckle noise and does not require holographic methods of registration. Second, the use of computer-synthesized phase diffractive elements allows you to generate required coding wave front and minimizes the loss of radiation in the system," commented the Associate Professor at the Institute of Laser and Plasma Technologies of the National Research Nuclear University MEPhI Vitaly Krasnov.