Cory W. Christenson

Holographic three-dimensional telepresence using large-area photorefractive polymer

Holography is a technique that is used to display objects or scenes in three dimensions. Such three-dimensional (3D) images, or holograms, can be seen with the unassisted eye and are very similar to how humans see the actual environment surrounding them. The concept of 3D telepresence, a real-time dynamic hologram depicting a scene occurring in a different location, has attracted considerable public interest since it was depicted in the original Star Wars film in 1977. However, the lack of sufficient computational power to produce realistic computer-generated holograms and the absence of large-area and dynamically updatable holographic recording media have prevented realization of the concept. Here we use a holographic stereographic technique and a photorefractive polymer material as the recording medium to demonstrate a holographic display that can refresh images every two seconds. A 50 Hz nanosecond pulsed laser is used to write the holographic pixels. Multicoloured holographic 3D images are produced by using angular multiplexing, and the full parallax display employs spatial multiplexing. 3D telepresence is demonstrated by taking multiple images from one location and transmitting the information via Ethernet to another location where the hologram is printed with the quasi-real-time dynamic 3D display. Further improvements could bring applications in telemedicine, prototyping, advertising, updatable 3D maps and entertainment.

An Updatable Holographic Display for 3D Visualization

Among the various methods to produce three-dimensional (3D) images, holography occupies a special niche. Indeed, holograms provide highly realistic 3D images with a large viewing angle capability without the need for special eyewear. Such characteristics make them valuable tools for a wide range of applications such as medical, industrial, military, and entertainment imaging. To be suitable for an updatable holographic display, a material needs to have a high diffraction efficiency, fast writing time, hours of image persistence, capability for rapid erasure, and the potential for large display area-a combination of properties that has not been realized before.

Roll‐to‐Roll Fabrication of Multilayer Films for High Capacity Optical Data Storage

Optical data storage (ODS) has led to transformative advances in information storage and distribution technology. Conventional two-dimensional ODS media have allowed storage capacities necessary for high-defi nition video. The capacity is limited, however, by the size of the disk and the number of layers that can be addressed using highly scattering phase-change materials employed in these media. [ 1 ] Here we report on a co-extrusion process for fabricating roll-to-roll multilayer (ML) fi lms for high-density ODS. This process can easily produce a continuous, complete storage medium hundreds of meters in length and meters in width, ready for fabrication into the standard 120 mm diameter disk or a variety of other potential formats, with total writable areas suffi cient for terabyte (TB) to petabyte (PB)-scale capacity. The co-extrusion process is also low-cost and far simpler than current manufacturing approaches, such as spin-coating [ 2 , 3 ] and lamination. [ 4–6 ] We demonstrate data storage in 23 layers of a 78 μ m thick ML fi lm using a continuous-wave Blu-Ray (BR) laser by fl uorescence (FL) quenching of an organic dye. The areal density is found to be similar to that of commercial disks, and the small layer spacing allowed by a FL-based scheme leads to a bit density of 1.2 × 10 12 cm − 3 . Given the mechanism and high axial density, the cross-talk during writing is also examined. The approach is generic so that materials already developed for high-density ODS can be exploited for innovations including “cloud”-scale data storage. Commercial ODS disks are made by fi rst injection molding of the thick, plastic substrate. The refl ective and active layers are added by a combination of sputtering and spin-coating. [ 1 ] For simple read/write systems based on a bit-wise one-photon write scheme, a multilayer architecture would require a multiplicity of steps with the current manufacturing processes. Several organic dye/polymer schemes suitable for three-dimensional

Grating dynamics in a photorefractive polymer with Alq 3 electron traps

The electron transporting molecule tris(8-hydroxyquinoline) aluminum (Alq(3)) was added in low concentrations to a photorefractive polymer composite to provide trapping sites for electrons. This sample exhibited larger two-beam coupling gain, higher diffraction efficiency at lower voltages, and an increased dielectric breakdown strength compared to a control sample. The dynamics also revealed the presence of a competing grating, and a bipolar charge transport model is shown to fit the data. Overall, Alq(3) improves the response time, efficiency, and breakdown voltage without a significant increase in absorption or loss of phase stability. This has applications for reflection displays and pulsed writing, where charge trapping and generation are major factors limiting the usefulness of photorefractive polymers.

Photorefractive performances of a graphene-doped PATPD/7-DCST/ECZ composite

Photorefractive polymer composites have gained considerable attention due to their fascinating applications like 3D displays and 3D Telepresence. In this report, the performance of a novel PR polymer composite doped with graphene is studied. The addition of graphene laminates to a photorefractive composite results in up to threefold enhancement of space charge (SC) field build-up time. From our optical and electrical measurements, the faster build-up time is attributed to larger charge generation resulting from electronic interaction between graphene and the 7-DCST chromophores.

Materials for an Updatable Holographic 3D Display

Holography is a powerful technique for providing high-resolution, realistic three-dimensional (3D) images without the need for special eyewear. A material that takes full advantage of the potential of holography, including updatability, has not existed. Here, the first updatable holographic 3D display based on a photorefractive polymer is summarized. The performance characteristics of these materials are measured, and how they relate to the development of additional display enhancements such as pulsed writing, white light viewing, and large viewing angle, are discussed.

Achieving enhanced gain in photorefractive polymers by eliminating electron contributions using large bias fields

Photorefractive polymers have been extensively studied for over two decades and have found applications in holographic displays and optical image processing. The complexity of these materials arises from multiple charge contributions, for example, leading to the formation of competing photorefractive gratings. It has been recently shown that in a photorefractive polymer at relatively moderate applied electric fields the primary charge carriers (holes) establish an initial grating, followed by a subsequent competing grating (electrons) resulting in a decreased two-beam coupling and diffraction efficiencies. In this paper, it is shown that with relatively large sustainable bias fields, the two-beam coupling efficiency is enhanced owing to a decreased electron contribution. These results also explain the cause of dielectric breakdown experienced under large bias fields. Our conclusions are supported by self-pumped transient two-beam coupling and photocurrent measurements as a function of applied bias fields at different wavelengths.

Interdigitated coplanar electrodes for enhanced sensitivity in a photorefractive polymer

Organic photorefractive polymer composites can be made to exhibit near 100% diffraction efficiency and fast writing times, though large external slants are needed to project the applied field onto the grating vector. We show here that the use of interdigitated electrodes on a single plane provides similar performance to these standard devices and geometries but without a external slant angle. This new devices structure also greatly improves the diffraction efficiency and sensitivity compared to less slanted standard devices necessary for some real applications, such as holographic displays, optical coherence imaging, and in-plane switching.

Time dynamics of self-pumped reflection gratings in a photorefractive polymer

The time dynamics of self-pumped reflection gratings in a commonly used photorefractive polymer PDCST:PVK:ECZ-BBP:C60 with no additional electron sources or traps is investigated. While holes are normally the mobile charges and responsible for grating formation, our experimental observations, analyzed using multi-exponential fitting curves, show evidence of electrons in addition to holes as charge carriers, particularly above an applied field of 40 V/μm. The dependence of effective carrier mobilities on the applied electric field, deduced from experimental results, show stronger field dependence of electron mobility at high electric fields. At an applied field of 70 V/μm, electron and hole mobilities become approximately equal, and the contribution of electrons on grating formation becomes significant.

Future of photorefractive based holographic 3D display

The very first demonstration of our refreshable holographic display based on photorefractive polymer was published in Nature early 20081. Based on the unique properties of a new organic photorefractive material and the holographic stereography technique, this display addressed a gap between large static holograms printed in permanent media (photopolymers) and small real time holographic systems like the MIT holovideo. Applications range from medical imaging to refreshable maps and advertisement. Here we are presenting several technical solutions for improving the performance parameters of the initial display from an optical point of view. Full color holograms can be generated thanks to angular multiplexing, the recording time can be reduced from minutes to seconds with a pulsed laser, and full parallax hologram can be recorded in a reasonable time thanks to parallel writing. We also discuss the future of such a display and the possibility of video rate.