Optical image hiding with a modified Mach–Zehnder interferometer

• The method developed a fully optical scheme for image hiding in a modified Mach–Zehnder interferometer.
• The hidden data are obtained by four-step phase-shifting interferometry in a modified Mach–Zehnder interferometer.
• The retrieved image data has been achieved digitally.
• The technique allows a high-speed image hiding through fully optical means.
• The method can be widely used on image secure transmission at high speed in Internet and image watermarking.

A method for optical image hiding in a Fresnel domain is proposed. In our modified Mach–Zehnder interferometer (MZI) architecture, an object beam is inserted into the object image to be hidden; the reference beam is produced by laser illumination through the phase plates and the host image. Afterwards, the reference beam is not only restricted to providing phase shifts in the hologram-recording process, but it can also add host image to engage the image hiding function. After two images experience Fresnel diffraction, the diffraction waves are registered as interference patterns on a CCD plane, which resembles a Fresnel diffraction pattern of the host image. The object image is embedded in the host image inside the Fresnel domain. Here, we present a theoretical analysis and preliminary experimental results for this method. It can be widely applied to secure image transmissions at a high speed over the internet and for image watermarking.