Brent Valle

Two-photon 3D optical data storage via aggregate switching of excimer-forming dyes.

N S Current optical data storage (ODS) technologies use onephoton-absorption processes to write data by locally changing the optical properties of the medium. [ 1 , 2 ] Since the lateral dimensions of spots that can be written are near the diffraction limit, signifi cant capacity increases require new approaches such as storage in three dimensions. DVDs, which comprise up to four individually addressable storage layers, exemplify the potential of this concept, but the complexity of producing and using multilayer systems increases with the number of layers. In bulk materials, changes can be confi ned in the third dimension via nonlinear optical processes, such as two-photon absorption (TPA). [ 3– 6 ] We have developed a novel ODS system that relies on the optically-induced switching of the aggregation state and fl uorescence of a TPA dye in a polymer matrix. Welldefi ned, ∼ 3 × 3 × 6 μ m-large voxels were written with single focused laser pulses and read by confocal laser scanning microscopy. Such ODS systems are easily produced and promise a storage capacity of up to several Tbytes on a DVD-size disk, which is ∼ 100× higher than that of current commercial ODS technologies. [ 6 , 7 ]

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

A melt-processable squaraine-based organic glass for nonlinear optics†

The synthesis and properties of a new indole-based squaraine dye functionalized with ethylhexyl substituents are reported. The chromophore displays a large two-photon absorption cross-section of ∼1490 GM at a resonance wavelength of 1160 nm. The crystalline material exhibits a melting temperature of 222 °C, which is sufficiently low to allow for melt-processing without significant thermal decomposition. Crystallization of the dye from the melt is exceedingly slow, so that amorphous glasses with a glass transition temperature of 60 °C can easily be produced, even without particularly rapid cooling. This allows the fabrication of thin films and more complex shapes, which offer a maximum of dye content, yet lack the scattering effects associated with organic crystalline materials.

Spectral aspects of cavity tuned absorption in organic photovoltaic films

Concentration of light and infrared capture are two favored approaches for increasing the power conversion efficiency (PCE) of photovoltaic devices. Using optical transfer matrix formalism, we model the absorption of organic photovoltaic films as a function of active layer thickness and incident wavelength. In our simulations we consider the absorption in the optical cavity formed by the polymer bulk heterojunction active layer (AL) between the aluminum cathode and indium tin oxide (ITO) anode. We find that optical absorption can be finely tuned by adjusting the ITO thickness within a relatively narrow range, thus eliminating the need for a separate optical spacer. We also observe distinct spectral effects due to frequency pulling which results in enhanced long-wavelength absorption. Spectral sculpting can be carried out by cavity design without affecting the open circuit voltage as the spectral shifts are purely optical effects. We have experimentally verified aspects of our modeling and suggest methods to improve device design.Concentration of light and infrared capture are two favored approaches for increasing the power conversion efficiency (PCE) of photovoltaic devices. Using optical transfer matrix formalism, we model the absorption of organic photovoltaic films as a function of active layer thickness and incident wavelength. In our simulations we consider the absorption in the optical cavity formed by the polymer bulk heterojunction active layer (AL) between the aluminum cathode and indium tin oxide (ITO) anode. We find that optical absorption can be finely tuned by adjusting the ITO thickness within a relatively narrow range, thus eliminating the need for a separate optical spacer. We also observe distinct spectral effects due to frequency pulling which results in enhanced long-wavelength absorption. Spectral sculpting can be carried out by cavity design without affecting the open circuit voltage as the spectral shifts are purely optical effects. We have experimentally verified aspects of our modeling and suggest methods to improve device design.

Functionalized cyano-OPVs as melt-processable two-photon absorbers

Several cyano-functionalized oligo(phenylenevinylene) (cyano-OPV) dyes were modified with different alkyl substituents with the objective to develop melt-processable, two-photon absorbing materials. The new dyes exhibit two-photon absorption cross-sections in the range of 400–850 GM, can be melt-processed at temperatures as low as ∼100 °C, and offer high thermal stability. The propensity of these molecules to form excimers also makes them interesting for sensor and data storage applications.

Multilayer films for optical data storage

The amount of digital information being generated has accelerated greatly over the past few decades. The proliferation of high-definition media, mobile devices, and improved image techniques has increased both the number and the size of files created. Some of this data requires only temporary storage, but the ever-expanding digital footprint of companies and individuals calls for long-term storage options. There are several technologies available to meet such demands. Flash memory is attractive for its fast data rate and portability, but it has limited read/write cycles and capacity. Spinning disk hard drives have become the most popular data storage medium due to increases in drive capacity and significant reductions in the cost per bit, but their lifetimes are insufficient for archival storage. Magnetic tapes can reach similarly high capacities and last for decades, but they have slow access times and require a relatively large initial investment in read/write hardware.1 Optical data storage (ODS) provides an inexpensive, portable alternative with fast access times and long lifetimes. The tradeoff for these advantages is in the comparatively low capacity of the format. Current state-of-the-art Blu-ray discs (BDs) can achieve up to 100GB/disc2 which, while sufficient for media, is not adequate for the large-scale archival data storage required by many companies and digitally-entrenched computer users. The capacity of ODS is limited by optics and disc material. Capacity increases from CD to DVD and, finally, BD were achieved using shorter wavelength lasers and higher numerical aperture (NA) optics. Writing in BDs is already performed with a 0.85NA lens at a near-UV wavelength, which limits further increases to the in-plane storage density. Furthermore, the axial storage density is limited by multiple reflections and large scattering of the inorganic phase-change materials employed in these discs, which permit only a few data layers within the disc volume.2 Figure 1. Schematic of the co-extruder used to produce the multilayer film. The buffer layer polymer and dye-doped active layer polymer are extruded into a bilayer feedblock and then passed through a series of multiplication dies, each of which double the number of layers. A final surface layer is added on both sides for mechanical stability. (Reprinted with permission from Eric Baer.)

Co-extruded multilayer films for high capacity optical data storage

New approaches for optical data storage (ODS) applications are needed to meet the future requirements of applications in multimedia, archiving, security, and many others. Commercial data storage technologies are moving to threedimensional (3D) materials, but the capacity is limited by the fabrication cost and the number of layers that can be addressed using the reflection-based storage mechanism. We demonstrate here storage systems based on co-extrusion of multilayer (ML) films that can overcome these problems. The organic roll-to-roll films produced can easily be produced hundreds of meters in length, in a far simpler and cheaper manner than current manufacturing methods such as spin coating and lamination. The medium consists of alternating active and buffer layers, and data storage is demonstrated by writing images in 23 layers of 78 μm thick films by fluorescence (FL) quenching of an organic dye. The areal data resolution is at the diffraction limit of the CW Blu-ray (BR) laser employed, and the co-extrusion technique allows for small layer spacings, leading to a total bit density 1.2 Tb/cm3. We anticipate materials already demonstrated successful for 3D ODS will be adapted to this technique, as well as new systems developed, to take full advantage of this medium.