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We propose a new technique for the optical encryption of gray-level optical images digitized into 8-bits binary data by ASCII encoding followed by QPSK modulation. We made an encrypted digital hologram with a security key by using 2-step phase-shifting digital holography, and the encrypted digital hologram is recorded on a CCD camera with 256 gray-level quantized intensities. With these encrypted digital holograms, the phase values are reconstructed by the same security key and are decrypted into the original gray-level optical image by demodulation and decoding. Simulation results show that the proposed method can be used for cryptosystems and security systems.

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We present a novel information or key encryption and transmission technique based on phase-shifting digital holography for a security system. Phase-shifting digital holography is used for recording phase and amplitude information on CCD device. 4-step phase-shifting is implemented by moving the PZT mirror with equidistant phase steps of π /2. The information and the key are converted to random phase patterns. Digital hologram in this method is Fourier transform hologram and quantized with 256 gray-level. The basic idea is that we reuse a 256 gray-level digital hologram to encrypt the information or the key with 4-step phase-shifting digital holography. The encrypted binary data/image in the form of digital hologram can be transmitted through communication network, and is reconstructed and decrypted digitally. The simulation shows that the proposed method gives good results for a successive encryption/transmission.

We propose a digital holographic interference analysis method based on a 2-frame phase-shifting technique for measuring an optical mirror surface. The technique using 2-frame phase-shifting digital interferometry is more efficient than multi-frame phase-shifting techniques because the 2-frame method has the advantage of a reduced number of interferograms, and then takes less time to acquire the wanted topography information from interferograms. In this measurement system, 2-frame phaseshifting digital interferograms are acquired by moving the reference flat mirror surface, which is attached to a piezoelectric transducer, with phase step of 0 or π/2 in the reference beam path. The measurements are recorded on a CCD detector. The optical interferometry is designed on the basis of polarization characteristics of a polarizing beam splitter. Therefore the noise from outside turbulence can be decreased. The proposed 2-frame algorithm uses the relative phase difference of the neighbor pixels. The experiment has been carried out on an optical mirror which flatness is less than λ/4. The measurement of the optical mirror surface topography using 2-frame phaseshifting interferometry shows that the peak-to-peak value is calculated to be about 0.1779 μm, the root-mean-square value is about 0.034 μm. Thus, the proposed method is expected to be used in nondestructive testing of optical components.