Adam C. Urness

Arbitrary GRIN component fabrication in optically driven diffusive photopolymers

We introduce a maskless lithography tool and optically-initiated diffusive photopolymer that enable arbitrary two-dimensional gradient index (GRIN) polymer lens profiles. The lithography tool uses a pulse-width modulated deformable mirror device (DMD) to control the 8-bit gray-scale intensity pattern on the material. The custom polymer responds with a self-developing refractive index profile that is non-linear with optical dose. We show that this nonlinear material response can be corrected with pre-compensation of the intensity pattern to yield high fidelity, optically induced index profiles. The process is demonstrated with quadratic, millimeter aperture GRIN lenses, Zernike polynomials and GRIN Fresnel lenses.

High dynamic range holographic data storage media

Holographic data storage (HDS) employs the physics of holography to record digital data in three dimensions in a highly stable photopolymer medium. The photopolymer medium must provide the essential characteristics of low scatter and high dynamic range while maintaining low recording induced physical shrinkage and long archival lifetimes. In this article, we report on media advancements employing Akonia’s DREDTM technology which provide a 5x increase in media dynamic range with unchanged media shrinkage. We also discuss the implications of these results for photopolymer media mechanistic models.

Quantitative modeling of the reaction/diffusion kinetics of two-chemistry diffusive photopolymers

A general strategy for characterizing the reaction/diffusion kinetics of photopolymer media is proposed, in which key processes are decoupled and independently measured. This strategy enables prediction of a material’s potential refractive index change, solely on the basis of its chemical components. The degree to which a material does not reach this potential reveals the fraction of monomer that has participated in unwanted reactions, reducing spatial resolution and lifetime. This approach is demonstrated for a model material similar to commercial media, achieving quantitative predictions of refractive index response over three orders of exposure dose (~1 to ~103 mJ cm−2) and feature size (0.35 to 500 μm).

Homodyne detection of holographic memory systems

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.

Holographic data storage at 2+ Tbit/in2

The onslaught of big data continues even as growth in data storage density tapers off. Meanwhile, the physics of holography continues to suggest the possibility of digital data storage at densities far exceeding those of today’s technologies. We report on recent results achieved with a demonstrator platform incorporating several new secondgeneration techniques for increasing holographic data storage (HDS) recording density and speed. Since the highest reported areal densities for hard disk drive products currently hover in the 1 Tbit/in2 range, we have adopted 2 Tbit/in2 as a milestone likely to generate interest in the technology. The demonstrator is based on an advanced pre-production prototype, and so inherits highly functional electronic, mechanical, and optical subsystems. It employs a high-NA monocular architecture with proven angle-polytopic multiplexing. The demonstrator design includes several second-generation innovations. The first, dynamic aperture multiplexing, greatly increases the number of multiplexed holograms. The second, the DREDTM medium formulation, provides dramatically higher dynamic range to record these holograms. These two features alone theoretically allow the demonstrator to exceed 2 Tbit/in2. Additionally, it is equipped with the capability of quadrature homodyne detection, permitting phase quadrature multiplexing (QPSK modulation), and the potential to further increase user capacity by a factor of four or more. The demonstrator has thus been designed to achieve densities supporting the multi-terabyte storage capacities required for competitive products, and to demonstrate the potential for Moore’s-Law growth for years to come.

Arbitrary 2D GRIN lens fabrication in diffusive photopolymers

We introduce a new method to make gradient index (GRIN) lenses in diffusive photopolymers with nearly arbitrary two-dimensional (2D) profiles. By modulating the 2D intensity pattern and power of the exposure with a deformable mirror device (DMD), the index profile of the GRIN lens can be controlled. Combined with the self-developing nature of the photophotopolymer, rapid on-demand printing of arbitrary micro-optics is enabled. We demonstrate the process by fabricating quadratic GRIN lenses, Zernike polynomials and multi-focal lenses.

Multi-terabit/in2 holographic data storage demonstration

We report on the demonstration of holographic data storage (HDS) at a raw areal bit density of 2.2 Tbit/in2. The demonstration was performed on a platform incorporating several new technical innovations. One key innovation – the coherent data channel – was successfully introduced ahead of schedule following encouraging early results. Issues of media recording efficiency and carrier wavefront demodulation for homodyne detection are discussed.

Multi-terabit/in2holographic data storage demonstration

We report on the demonstration of holographic data storage (HDS) at a raw areal bit density of 2.2 Tbit/in2. The demonstration was performed on a platform incorporating several new technical innovations. One key innovation – the coherent data channel – was successfully introduced ahead of schedule following encouraging early results. Issues of media recording efficiency and carrier wavefront demodulation for homodyne detection are discussed.

Multi-terabit/in 2 holographic data storage demonstration

We report on the demonstration of holographic data storage (HDS) at a raw areal bit density of 2.2 Tbit/in2. The demonstration was performed on a platform incorporating several new technical innovations. One key innovation – the coherent data channel – was successfully introduced ahead of schedule following encouraging early results. Issues of media recording efficiency and carrier wavefront demodulation for homodyne detection are discussed.

Liquid deposition photolithography for the fabrication of gradient index (GRIN) micro-optics

One photon diffusive photopolymers enable self-developing three dimensional (3D) refractive index patterning of up to cm thick solid volumes for the fabrication of micro-optics. However, one photon absorption in solid, thick materials does not yield complete control of the 3D refractive index distribution due to diffraction and the excessive development time for index features measuring 100’s of microns in diameter or larger. We present a fabrication method and photopolymer formulation that can efficiently create mm3 optical devices with programmable, gradient index of refraction with arbitrary feature size and shape. Index contrast of 0.1 is demonstrated, which is 20 times larger than commercial holographic photopolymers. Devices are fabricated by repetitive micro-fluidic layering of a self-developing photopolymer structured by projection lithography. The process has the unusual property that total fabrication time for a fixed thickness decreases as the number of layers is increased, reducing the fabrication time for high axial resolution micro-optics. We demonstrate the process by fabricating thick waveguide arrays and gradient index lenses.