A phase-only encryption/decryption scheme with the readout based on the zeroth-order phase-contrast technique (ZOPCT), without the use of a phase-changing plate on the Fourier plane of an optical system based on the 4f optical correlator, is proposed. The encryption of a gray-level image is achieved by multiplying the phase distribution obtained directly from the gray-level image by a random phase distribution. The robustness of the encoding is assured by the nonlinearity intrinsic to the proposed phase-contrast method and the random phase distribution used in the encryption process. The experimental system has been implemented with liquid-crystal spatial modulators to generate phase-encrypted masks and a decrypting key. The advantage of this method is the easy scheme to recover the gray-level information from the decrypted phase-only mask applying the ZOPCT. An analysis of this decryption method was performed against brute force attacks.
An encryption/decryption scheme based on a new Phase-Contrast Technique, without the use of a phase-changing plate (phase dielectric dot) on the Fourier plane of a 4f optical correlator is proposed. The encryption of a gray level image is achieved by multiplying the phase distribution obtained directly from the gray level image by a random phase distribution. The encoding is obtained without any iterative calculation to generate the encrypted phase-only mask. The robustness of the encoding is assured by the non-linearities intrinsic to the phase-contrast method and the random phase distribution used in the encryption process. The advantage of this method is the easy scheme to recover the gray level information from the decrypted phase-only mask applying the proposed Zero-Order Phase-contrast Technique.
A laser triangulation range finder based on a chaotic and detection scheme is presented. An elementary non-linear electronic oscillator composed by two operation amplifiers with feedback current form two antiparallel diodes generates a chaotic signal that is used to generate a chaotic clock modulation with a well-defined broad band spectrum. This chaotic clock modulates a laser beam that is transmitted and received by a collecting optics in a laser triangulation range finder scheme. A band limited phase delay equalized amplifier sends the received signal to a balanced demodulator using the same chaotic generated signal as 'local oscillator'. A low pass filter is tuned to assure good compromise against noise immunity and the desired response speed. This modulator scheme allows several laser stations to operate in same working area, avoiding carefully adjusted field-of-view screening and cross-detection false alarm due to the interference of other laser stations. The chaotic modulator can be used as an alternative for microprocessor based pseudo random sequence generator when board space or cost is a critical system specification. The laser triangulation range finder has a range of 0.5m to 2m using a 3mW class IIIa visible laser, with precision of 5 mm.
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