This PDF file contains the front matter associated with SPIE Proceedings Volume 9201 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

To compete in the archive and backup industries, holographic data storage must be highly competitive in four critical areas: total cost of ownership (TCO), cost/TB, capacity/footprint, and transfer rate. New holographic technology advancements by Akonia Holographics have enabled the potential for ultra-high capacity holographic storage devices that are capable of world record bit densities of over 2-4Tbit/in², up to 200MB/s transfer rates, and media costs less than $10/TB in the next few years. Additional advantages include more than a 3x lower TCO than LTO, a 3.5x decrease in volumetric footprint, 30ms random access times, and 50 year archive life. At these bit densities, 4.5 Petabytes of uncompressed user data could be stored in a 19” rack system. A demonstration platform based on these new advances has been designed and built by Akonia to progressively demonstrate bit densities of 2Tb/in², 4Tb/in², and 8Tb/in² over the next year. Keywords: holographic

This paper introduces a method to reconstruct a polarization hologram recorded by dual-channel polarization holography. In this method, simultaneously reconstructed two images with p- and s-polarization components are captured by an image sensor with p- and s-polarized plane waves. The principle is explained and numerically verified.

We formalize the theoretical effects of optical resonator enhancement on diffraction efficiency, read rate, and write rate of plane wave holograms, with a view toward page based holographic data storage. Trade-offs in cavity enhancement are also examined. Theory predicts ~160% of enhancement in diffraction efficiency is feasible when power loss of the hologram is ~8% and diffraction efficiency is ~8%. We report experimental verification of ~30% enhancement of diffraction efficiency for a hologram written in 0.03% Fe:LiNbO3 (Deltronic Crystal Industries, Inc.) with a 532 nm wavelength, pulsed, DPSS, Nd-YAG, laser and read by a red He-Ne laser. The Bragg selectivity width under the cavityenhanced readout is experimentally confirmed to be unaffected by cavity enhancement, and it agrees with theoretical prediction.

Pulsed Heat Assisted Magnetic Recording (HAMR) is being developed to improve HAMR reliability. In conventional HAMR systems the laser is on and at a fixed power during the writing of the entire sector. In a pulsed HAMR implementation, the laser is turned on and off during the bit cell. For example, for a 50% duty cycle, the laser is on for half the bit cell and off for the remainder of the bit cell. Unlike traditional HAMR where the transitions are formed when the magnetic writer switches, in a pulsed implementation the transitions are formed during the pulsing of the laser. In this paper we show spin stand and drive recording performance of pulsed HAMR systems and compare the outcome to conventional recording. In particular, we show the importance and sensitivity of having proper alignment between the phase of the optical and magnetic signals and their effect on bit error rate (BER).

Heat assisted magnetic recording (HAMR) is expected to increase the storage areal density to more than 1 Tb/in² in hard disk drives (HDDs). In this technology, a laser is used to heat the magnetic media to the Curie point (~400-600 °C) during the writing process. The lubricant on the top of a magnetic disk could evaporate and be depleted under the laser heating. The change of the lubricant can lead to instability of the flying slider and failure of the head-disk interface (HDI). In this study, a HAMR test stage is developed to study the lubricant thermal behavior. Various heating conditions are controlled for the study of the lubricant thermal depletion. The effects of laser heating repetitions and power levels on the lubricant depletion are investigated experimentally. The lubricant reflow behavior is discussed as well.

We propose to develop a new method of information storage to replace magnetic hard disk drives and other instruments of secondary/backup data storage. The proposed method stores petabytes of user-data in a sugar cube (1 cm3), and can read/write that information at hundreds of megabits/sec. Digital information is recorded and stored in the form of a long macromolecule consisting of at least two bases, 𝐴 and 𝐵. (This would be similar to DNA strands constructed from the four nucleic acids 𝐺, 𝐶, 𝐴, 𝑇.) The macromolecules initially enter the system as blank slates. A macromolecule with, say, 10,000 identical bases in the form of 𝐴𝐴𝐴𝐴𝐴. . . . 𝐴𝐴𝐴 may be used to record a kilobyte block of user-data (including modulation and error-correction coding), although, in this blank state, it can only represent the null sequence 00000....000. Suppose this blank string of 𝐴’s is dragged before an atomically-sharp needle of a scanning tunneling microscope (STM). When electric pulses are applied to the needle in accordance with the sequence of 0s and 1s of a 1 𝑘𝐵 block of user-data, selected 𝐴 molecules will be transformed into 𝐵 molecules (e.g., a fraction of 𝐴 will be broken off and discarded). The resulting string now encodes the user-data in the form of 𝐴𝐴𝐵𝐴𝐵𝐵𝐴. . . 𝐵𝐴𝐵. The same STM needle can subsequently read the recorded information, as 𝐴 and 𝐵 would produce different electric signals when the strand passes under the needle. The macromolecule now represents a data block to be stored in a “parking lot” within the sugar cube, and later brought to a read station on demand. Millions of parking spots and thousands of Read/Write stations may be integrated within the micro-fabricated sugar cube, thus providing access to petabytes of user-data in a scheme that benefits from the massive parallelism of thousands of Read/Write stations within the same three-dimensionally micro-structured device.

Results of implementation of technical solution for long term data storage technology on the basis of single crystal sapphire are presented. The effect of birefringence on the distribution of the focused laser beam through a uniaxial birefringent medium having a vertical orientation of the optical axis is analyzed. An expression for the calculation of the geometric aberrations of the focused laser beam in single-crystal substrate of the optical disc has been presented. It is shown that the problem of data reading through a substrate of negative single crystal sapphire can be solved by using for reading a special optical system with a plate of positive single crystal materials. The experimental results confirm the efficiency of the proposed technical solution.

We have developed a holographic data storage system that can demonstrate real-time playback of beyond high definition video signals. In the proposed system, to increase the data-transfer rate of the reproduced data, we focused on improving the SNR of the reproduced data and on improving the signal processing speed, which the SNR of the reproduced data has a significant effect on. One of the factors that deteriorate the SNR is shrinkage in the medium. This shrinkage distorts recorded holograms and degrades the quality of the reproduced data. We investigated wavefront compensation as a means to improve the SNR of reproduced data degraded by hologram distortion and found that controlling the defocus component of the reference beam is effective. We have also been developing parallel signal processing to increase the data-transfer rate. We placed three GPUs in the signal processing unit: one for the reproduced data detection from the reconstructed image and two for the LDPC decoding for error correction of the reproduced data. The LDPC decoding required a lot more time than the data detection, so we designed a signal processing in which detected data in the GPU for the data detection were sent to the two GPUs for the LDPC decoding alternatively. We implemented wavefront compensation for the defocus component and developed parallel signal processing with three GPUs for our holographic data storage system. Using this system, we demonstrated real-time playback of beyond high definition video signals with 50 Mbps.

The shifting tolerance of the collinear holographic data storage system is discussed considering its influences on the quality of the reconstructed data pages and the precision of the holographic disk actuator. The diffractive efficiencies with shifting along the x-axis and the z-axis are calculated respectively based on the bit error rates of the reconstructed data pages. The numerical aperture of the objective lens and the recording wavelength show different impacts on the shifting tolerance and the storage density. The orthogonal reference pattern shift multiplexing method is investigated. It is proved that the method could improve the data storage density by keeping the shifting tolerance.

The influence of various types of aberrations of recording and readout beams on the signal-to-noise ratio of the readout signal in microholographic recording was investigated through a numerical simulation. The simulation conditions were that the wavelength of the laser was 405 nm and the numerical aperture of the objective lenses was 0.85. The tolerance of the root-mean-square (RMS) wavefront aberrations was defined as the aberration when the signal-to-noise ratio with aberrations was comparable to that without aberrations. When both the recording and readout beams were aberrated and the signs of the aberrations were in the worst case, the tolerance of the RMS wavefront aberrations was 0.035λ regardless of the types of aberrations, which was half of the Maréchal’s criterion. Moreover, when the RMS wavefront aberrations of the recording and readout beams were within the above value and the signal-to-noise ratio of 2 was allowed, the bit intervals of 0.15 and 0.75 μm in the in-plane and vertical directions, respectively, which correspond to the recording density of 59 bit/μm³ (recording capacity of 10 TB), were shown to be feasible for confocal detection.

Heat assisted magnetic recording (HAMR) requires a sufficiently small heat spot, which is much below the diffraction limit of the wavelength of the used light. This can be achieved with an optical near field source consisting of a small metallic wedge which supports edge plasmons. The power transfer between a dielectric rectangular waveguide and this metallic wedge is investigated in simulations and experiments. Beating of two eigenmodes of this system leads to power oscillations between the waveguide core and the edge plasmon along their overlap length. This was confirmed in near field experiments which are based on the evaporation of phase change material with the absorbed optical near fields as heat source. Devices with weak and strong edge plasmon excitation could be clearly distinguished in a simple far field experiment.

Recent recording areal density and integrated drive performance demonstrations using Heat Assisted Magnetic Recording (HAMR) suggest that it is a viable technology to succeed conventional magnetic recording. However challenges still remain for the near field transducer, in particular reliability and sufficient thermal confinement. We explore a new NFT design, Near field Transducer Gap (NTG), which offers the potential to mitigate some of the issues in track confinement and thermal profile compared to earlier published studies [4]. The design offers efficiency improvements, and the potential to reduce unwanted background light and heating that can lead to erasure in the writing track, and neighbors.

We report using Inverse Electromagnetic Design to computationally optimize the geometric shapes of metallic optical antennas or near-field transducers (NFTs) and dielectric waveguide structures that comprise a sub-wavelength optical focusing system for practical use in Heat Assisted Magnetic Recording (HAMR). This magnetic data-recording scheme relies on focusing optical energy to locally heat the area of a single bit, several hundred square nanometers on a hard disk, to the Curie temperature of the magnetic storage layer. There are three specifications of the optical system that must be met to enable HAMR as a commercial technology. First, to heat the media at scan rates upward of 10 m/s, ~1mW of light (<1% of typical laser diode output power) must be focused to a 30nm×30nm spot on the media. Second, the required lifetime of many years necessitates that the nano-scale NFT must not over-heat from optical absorption. Third, to avoid undesired erasing or interference of adjacent tracks on the media, there must be minimal stray optical radiation away from the hotspot on the hard disk. One cannot design the light delivery system by tackling each of these challenges independently, because they are governed by coupled electromagnetic phenomena. Instead, we propose multiobjective optimization using Inverse Electromagnetic Design in conjunction with a commercial 3D FDTD Maxwell’s equations solver. We computationally generated designs of a metallic NFT and a high-index waveguide grating that meet the HAMR specifications simultaneously. Compared to a mock industry design, our proposed design has a similar optical coupling efficiency, ~3x improved suppression of stray optical radiation, and a 60% (280°C) reduction in NFT temperature rise. We also distributed the Inverse Electromagnetic Design software online so that industry partners can use it as a repeatable design process.

In recent years, the commercial impact of optical data storage systems has been displaced by new technologies. Historically, optical data storage displaced older technologies, like consumer magnetic tape, so it is not unexpected that the same fate could pass optical data storage technology into the “retro” domain. In this paper, the basic building blocks of optical data storage are discussed, and limits based on current understanding are presented. Then, conceptual and philosophical arguments are presented to direct intuition toward future possibilities that may provide avenues to develop displacement data storage technology. For example, current understanding puts minimum practical data mark transverse dimensions in the range of 10nm by 10nm, regardless of recording technology. At the conservative assignment of 1 bit per mark area, this mark size equates to about 6,500 Gb/in² (10⁹ bits per square inch) of surface area. In order to gain the attention of research investment, displacement technologies need to target a 100X improvement in data density or about 1nm by 1nm mark size, with an effective surface data density of over 650,000 Gb/in². Research and engineering mindsets for displacement data storage technologies should address this goal to be considered significant. Otherwise, advancements in known technologies will probably evolve to satisfy demand.

Nano-scale resolution in miniature optical systems has been realized in the optical data storage industry. Numerical apertures greater than unity have been achieved in by utilizing the high index material of a hemispherical Solid Immersion Lens (SIL), which increases the resolution of the backing objective by a factor that is related to the refractive index of the SIL. In this research, a custom Hyper-Blu-Disc (HBD) NA=1.4 SIL objective is utilized for high-fidelity readout of data pits beneath a 100μm thick cover layer on an optical Blu-Ray Disc. If realized commercially, the increase in data density could be 3X today’s Blu-Ray technology. A distinct difference between this work and other work with SILs in optical data storage is the relatively thick cover layer of 100μm. Recently, there has been interest in discovering new ways to apply the technology and methods used in optical data storage for other means. The inherent design of the HBD objective to image through a shallow layer of dielectric material may lend itself to be used as an effective means for characterizing subsurface damage in optical materials. This research will furthermore investigate the HBD objective as a means of detecting subsurface damage.

This paper presents the decoupling direct tracking control method for the super multi-layer optical disk. The disk includes multiple recording layers and a servo layer with a guiding groove, and data is recorded on each recording layer right above the groove of the servo layer by using two laser beams. However, some disturbances such as disk tilt or lens shift might cause displacement between the two focal points. And due to scratches or finger prints on the disk surface, two focal point’s coupling actions destabilize the tracking control. We developed new tracking control method for preventing any displacement and destabilization by the coupling action.

The method of high-density data recording by laser thermo-lithography with ion-beam etching was proposed. The nanocomposite films were created by the spin-coating method on basis of organic positive photoresist and added synthesized dyes characterized by absorption in the spectral region 390-410 nm and which are able to be evaporated by 405 nm laser radiation. The pits with 250 – 300 nm width were performed on the thin organic nanocomposite films by 405 nm laser beam focused by 0.85 NA lens. The organic nanocomposite film with obtained pits was used as a mask for reactive ion-beam etching of glass substrate. The 150 nm pits were performed on the substrate surface in the result of the laser thermo-lithography with ion-beam etching.

Holographic data storage (HDS) remains an attractive technology for big data. We report on recent results achieved with a demonstrator platform incorporating several new second-generation techniques for increasing HDS recording density and speed. This demonstrator has been designed to achieve densities that support the multi-terabyte storage capacities required for a competitive product. It leverages technology from an existing state-of-the-art pre-production prototype, while incorporating a new optical head designed to demonstrate several new technical advances. The demonstrator employs the new technique of dynamic aperture multiplexing in a monocular architecture. In a previous report, a monocular system employing angle-polytopic multiplexing achieved a recording density over 700 Gbit/in², exceeding that of contemporaneously shipping hard drives [1]. Dynamic aperture multiplexing represents an evolutionary improvement with the potential to increase this figure by over 200%, while still using proven anglepolytopic multiplexing in a monocular architecture. Additionally, the demonstrator is capable of two revolutionary advances in HDS technology. The first, quadrature homodyne detection, enables the use of phase shift keying (PSK) for signal encoding, which dramatically improves recording intensity homogeneity and increases SNR. The second, phase quadrature holographic multiplexing, further doubles density by recording pairs of holograms in quadrature (QPSK encoding). We report on the design and construction of the demonstrator, and on the results of current recording experiments.

Holographic data storage (HDS) is a promising technology that has huge capacity. A multiplexing method plays a significant role in increasing the data capacity. Various multiplexing methods have been researched so far. In this paper, we proposed shift-peristrophic multiplexing using spherical reference wave and experimentally verified that this method is efficiently increase the data capacity. A series of holograms was recorded with shift multiplexing and rotating recording material with the axis of rotation being perpendicular to the material's surface. This method can realize more than 1 Tbits/inch² data density recording. Furthermore if we maximize the performance of a recording medium, several TB per disk capacity would be available.

We present a homodyne detection system implemented for a page-wise holographic memory architecture. Homodyne detection by holographic memory systems enables phase quadrature multiplexing (doubling address space), and lower exposure times (increasing read transfer rates). It also enables phase modulation, which improves signal-to-noise ratio (SNR) to further increase data capacity. We believe this is the first experimental demonstration of homodyne detection for a page-wise holographic memory system suitable for a commercial design.

An optical storage system which stores data in three spacial and three physical dimensions is designed and investigated. Its feasibility has been demonstrated by theoretical derivation and numerical calculation. This system has comprehensive advantages including very large capacity, ultrafast throughputs, relatively simple structure and compatibility with CD and DVD. It’s an actually practicable technology. With two-photon absorption writing/erasing and optical coherence tomography reading, its storage capacity is over 32 Tbytes per DVD sized disk, and its reading speed is over 25 Gbits/s with high signal-to-noise ratio of over 76 dB. The larger capacity of over 1 Pbyte per disk is potential.

Results of numerical simulation of near-field optical data storage using microstrip probe are presented. Simulation is carried out on the basis of the finite-difference time-domain method. Features of the information reading process from the ROM and RW (based on the phase transmissions of Ge₂Sb₂Te₅ film) formats of optical discs under illumination and illumination-collection mode are analyzed and considered. Mathematical modeling has shown that the signal from the ROM-format disc under illumination mode, despite the fact that the probe has a significant far-field transmission coefficient, has a large crosstalk and small spatial resolution (significantly worse than a size of probe aperture). Unlike illumination mode, signal under illumination-collection mode (pure near-field method) has a resolution close to the size of the aperture, good amplitude and contrast, as well as relatively low crosstalk. However, information reading under illumination-collection mode from RW-format disc is not able to get the same good quality signal. Therefore the further optimization of the method is required to improve the signal quality of RW format.