Improved phase hologram generation of multiple 3D objects.

We demonstrate the generation of phase holograms of multiple 3D objects at different axial positions without cross talk and significant improvements in performance over conventional methods. We first obtain the phase hologram of two 3D objects, each one comprising 50 layers, using the global Gerchberg-Saxton algorithm. Then, we discuss and demonstrate a propagation approach based on the singular value decomposition of the Fresnel impulse response function that enables fast computation of small distance propagations.

Alternative constraints for improved multiplane hologram generation.

In this work, we introduce a modified hologram plane constraint to improve the accuracy of the global Gerchberg-Saxton (GGS) algorithm used for multiplane phase-only hologram generation. This constraint consists of a modified phase factor that depends on the amplitude of the field in the hologram plane. We demonstrate that this constraint produces an increase in the mean correlation coefficient between the reconstructed planes from a multiplane hologram and the corresponding amplitude targets for each plane.

Mixed constraint in global and sequential hologram generation.

In this paper, we implement a mixed constraint scheme with a global Gerchberg-Saxton algorithm for the improved generation of phase holograms from multiplane intensity distributions. We evaluate the performance of the proposed method compared to the mixed constraint sequential Gerchberg-Saxton algorithm, as well as the implementation of both schemes in several scenarios involving intensity distributions of up to nine independent planes. We also show that a careful selection of the parameters involved in the mixed constraint hologram generation technique can lead to even greater improvements in reconstruction quality.

Compression of 3D dynamic holographic scenes in the Fresnel domain.

In this paper we present an optodigital protocol for the compression of 3D dynamic scenes recorded with an off-axis Fresnel holographic system. The compression protocol involves optical scaling, sampling with binary masks, and multiplexing of the optical field data obtained after a filtering process applied to Fresnel holograms. Volume reduction of up to 93.

Noniterative multiplane holographic projection.

In this paper, we introduce a mixed complex and phase-only constraint for noniterative computer generation of phase-only holograms from multiplane intensity distributions. We are able to reproduce three-dimensional intensity distributions with the same number of planes achieved with the Gerchberg-Saxton (GS) algorithm; at the same time, we maintain the fast computation time of a noniterative method. In this way, we enable the possibility of multiplane light field control in dynamic applications.

Optimized random phase tiles for non-iterative hologram generation.

In this work, we introduce a technique for fast, high-quality, non-iterative generation of phase-only holograms from both 2D and 3D scenes. In this technique, we generate an optimized random phase tile which behaves like a small diffuser, spreading the amplitude of a section of the scene throughout the hologram plane. Each section of the scene is multiplied by this tile and then propagated to the hologram plane by means of the Fresnel transform.

Synthetic amplitude for improved reconstruction of noniterative phase holograms.

In this paper, we show how a specially designed synthetic amplitude can be used to obtain greatly improved reconstruction of objects only using the phase data of their Fourier or Fresnel transforms. The reconstruction of objects from phase-only information is of interest because phase modulation has much higher efficiency than amplitude modulation and can be achieved with a high degree of precision with current liquid-crystal-on-silicon spatial light modulators. However, direct reconstruction of an object from its phase information usually results in severely degraded outputs.

Optimized random phase encryption.

We propose for the first time, to the best of our knowledge, the use of optimized random phases (ORAPs) in a double random phase encryption scheme (DRPE). In DRPE schemes the convolution between two random phase functions encrypts the information to be secured. However, in actual encryption applications, this convolution of random phases also results in unwanted effects like speckle noise.

Optimized random phase only holograms.

We propose a simple and efficient technique capable of generating Fourier phase only holograms with a reconstruction quality similar to the results obtained with the Gerchberg-Saxton (G-S) algorithm. Our proposal is to use the traditional G-S algorithm to optimize a random phase pattern for the resolution, pixel size, and target size of the general optical system without any specific amplitude data. This produces an optimized random phase (ORAP), which is used for fast generation of phase only holograms of arbitrary amplitude targets.

Experimental optical encryption of grayscale information.

In this paper, we present a new protocol for achieving lower noise and consequently a higher dynamic range in optical encryption. This protocol allows for the securing and optimal recovery of any arbitrary grayscale images encrypted using an experimental double random phase mask encoding (DPRE) cryptosystem. The protocol takes advantage of recent advances that help reduce the noise due to the correlation of random phase mask in the decryption procedure and introduces the use of a "reference mask" as a reference object used to eliminate the noise due to the complex nature of the masks used in experimental DRPE setups.

Three-dimensional joint transform correlator cryptosystem.

We introduce for the first time, to the best of our knowledge, a three-dimensional experimental joint transform correlator (JTC) cryptosystem allowing the encryption of information for any 3D object, and as an additional novel feature, a second 3D object plays the role of the encoding key. While the JTC architecture is normally used to process 2D data, in this work, we envisage a technique that allows the use of this architecture to protect 3D data. The encrypted object information is contained in the joint power spectrum.

Experimental scrambling and noise reduction applied to the optical encryption of QR codes.

In this contribution, we implement two techniques to reinforce optical encryption, which we restrict in particular to the QR codes, but could be applied in a general encoding situation. To our knowledge, we present the first experimental-positional optical scrambling merged with an optical encryption procedure. The inclusion of an experimental scrambling technique in an optical encryption protocol, in particular dealing with a QR code "container", adds more protection to the encoding proposal.

Experimental QR code optical encryption: noise-free data recovering.

We report, to our knowledge for the first time, the experimental implementation of a quick response (QR) code as a "container" in an optical encryption system. A joint transform correlator architecture in an interferometric configuration is chosen as the experimental scheme. As the implementation is not possible in a single step, a multiplexing procedure to encrypt the QR code of the original information is applied.

Optical encryption and QR codes: secure and noise-free information retrieval.

We introduce for the first time the concept of an information "container" before a standard optical encrypting procedure. The "container" selected is a QR code which offers the main advantage of being tolerant to pollutant speckle noise. Besides, the QR code can be read by smartphones, a massively used device.

Multiplexing of encrypted data using fractal masks.

In this Letter, we present to the best of our knowledge a new all-optical technique for multiple-image encryption and multiplexing, based on fractal encrypting masks. The optical architecture is a joint transform correlator. The multiplexed encrypted data are stored in a photorefractive crystal.

Master key generation to avoid the use of an external reference wave in an experimental JTC encrypting architecture.

In experimental optodigital encrypting architectures, the use of a reference wave is essential. In this contribution, we present an experimental alternative to avoid the reference wave during the encrypting procedure in a joint transform correlator architecture by introducing the concept of a master key. Besides, the master key represents an additional security element for the entire protocol.

Experimental multiplexing of encrypted movies using a JTC architecture.

We present the first experimental technique to encrypt a movie under a joint transform correlator architecture. We also extend the method to multiplex several movies in a single package. We use a Mach-Zehnder interferometer to encrypt experimentally each movie.

Optical smart packaging to reduce transmitted information.

We demonstrate a smart image-packaging optical technique that uses what we believe is a new concept to save byte space when transmitting data. The technique supports a large set of images mapped into modulated speckle patterns. Then, they are multiplexed into a single package.

Pure optical dynamical color encryption.

We introduce a way to encrypt-decrypt a color dynamical phenomenon using a pure optical alternative. We split the three basic chromatic channels composing the input, and then each channel is processed through a 4f encoding method and a theta modulation applied to the each encrypted frame in every channel. All frames for a single channel are multiplexed.

All-optical encrypted movie.

We introduce for the first time the concept of an all-optical encrypted movie. This movie joints several encrypted frames corresponding to a time evolving situation employing the same encoding mask. Thanks to a multiplexing operation we compact the encrypted movie information into a single package.

Known-plaintext attack on a joint transform correlator encrypting system.

We demonstrate in this Letter that a joint transform correlator shows vulnerability to known-plaintext attacks. An unauthorized user, who intercepts both an object and its encrypted version, can obtain the security key code mask. In this contribution, we conduct a hybrid heuristic attack scheme merge to a Gerchberg-Saxton routine to estimate the encrypting key to decode different ciphertexts encrypted with that same key.

Noise-free recovery of optodigital encrypted and multiplexed images.

We present a method that allows storing multiple encrypted data using digital holography and a joint transform correlator architecture with a controllable angle reference wave. In this method, the information is multiplexed by using a key and a different reference wave angle for each object. In the recovering process, the use of different reference wave angles prevents noise produced by the nonrecovered objects from being superimposed on the recovered object; moreover, the position of the recovered object in the exit plane can be fully controlled.

Efficient encrypting procedure using amplitude and phase as independent channels to display decoy objects.

Objects acting as inputs of encrypting optical systems can be regarded as having two independent channels: amplitude and phase. In this context, we can use the term "complex objects" to refer these input objects. In this work we explore the way to perform an undercover operation where one channel (amplitude) is used to depict decoy information to confuse intruders, while the other (phase) operates with the true information.

Wavelength multiplexing encryption using joint transform correlator architecture.

We show that multiple secure data recording under a wavelength multiplexing technique is possible in a joint transform correlator (JTC) arrangement. We evaluate both the performance of the decrypting procedure and the influence of the input image size when decrypting with a wavelength different from that employed in the encryption step. This analysis reveals that the wavelength is a valid parameter to conduct image multiplexing encoding with the JTC architecture.

Optical-data storage-readout technique based on fractal encrypting masks.

We propose the use of fractal structured diffractive masks as keys in secure storage-readout systems. A joint transform correlator based on a photorefractive crystal in the Fourier domain is implemented to perform encryption and decryption. We discuss the advantages of encrypting information using this kind of deterministic keys in comparison to conventional random phase masks.