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Compared with other imaging probes such as fluorescent dyes and quantum dots, second-harmonic radiating imaging probes (SHRIMPs) provide a unique ultrafast, coherent optical contrast that is free of photobleaching and emission intermittency. Using the second-harmonic signal emitted from SHRIMPs, harmonic holography achieves three-dimensional holographic imaging with a color contrast similar to fluorescence microscopy where the uninterested background scattering is efficiently suppressed by an optical filter. The coherent contrast provided by SHRIMPs also enables imaging through turbid media via digital phase conjugation. Here we review the developments and applications of SHRIMPs and harmonic holography.

We present an experimental comparison of optical tomography techniques: Learning Tomography (LT), an iterative method based on beam propagation model and diffraction tomography (DT) based Born and Rytov approximation. Imaging experiments were performed on yeast cells clusters fixed in a transparent agarose gel. In particular, we compare the LT with a similar iterative but linear method based on Rytov approximation.

It is possible to focus coherent light through a multicore fiber with a resolution finer than the core-to-core spacing using digital phase conjugation. In this paper we use the memory effect and show that the displacement of the focus spot can be realized simply by tilting the beam incident on the multicore fiber. We demonstrate high-resolution imaging and pattern projection with a calibration procedure consisting of the acquisition of a single digital hologram.

The large number of modes supported by multimode optical fibers potentially allows the transmission of larger amounts of information compared to single mode fibers. However, when pulsed light is transmitted through multimode fibers, the spatio-temporal profile of the incident beam is altered upon propagation, leading to a highly scrambled spatial profile and a broadened temporal duration due to modal and material dispersion. We present a digital phase conjugation method to counter-propagate through a multimode optical fiber only a group of modes of similar propagation constants which interfere constructively at a single location at the other side of the fiber, generating a spatially focused pulse. Since only modes with the same speed are excited, temporal broadening due to modal dispersion is suppressed, preserving the ultrashort duration of the propagating pulse. Using this technique, we experimentally demonstrate the transmission of focused pulses of 500 fs through a 30 cm length, 200 micrometer core step-index multimode fiber. Additionally, using a graded-index fiber, which allows the propagation of a larger number of modes of the same speed than a graded index fiber (hence a better focusing capability), we have been able to deliver and scan high-intensity focused femtosecond pulses. Moreover, based on the described principle, we demonstrate for the first time two-photon excitation imaging through a multimode optical fiber.

We describe a holographic technique capable of sampling dynamic events at 150 femtosecond time resolution. We apply the technique to the study of the nonlinear propagation of high energy pulses through gas and condensed media. The holograms are recorded as a digitized image from a CCD camera and reconstructed numerically to retrieve the refractive index change during the nonlinear optical process. We show dramatic differences in the pulse propagation characteristics depending on the strength of the nonlinear coefficient of the material and it's time response. Both positive and negative index changes have been measured in different media. The holographic technique allows us to distinguish the very fast positive index changes that are generally attributable to the Kerr nonlinearity from the negative index changes that result from free electrons generated by multiphoton ionization.

"Optofluidics" is the marriage of optics, optoelectronics and nanophotonics with fluidics. Such integration represents a new approach for dynamic manipulation of optical properties at length scales both greater than and smaller than the wavelength of light with applications ranging from reconfigurable photonic circuits to fluidically adaptable optics to high sensitivity bio-detection currently under development. The capabilities in terms of fluidic control, mixing, miniaturization and optical property tuning afforded by micro-, nano- and electro-fluidics combined with soft lithography based fabrication provides an ideal platform upon which to build such devices. In this paper we provide a general overview of some of the important issues related to the fabrication, integration and operation of optofluidic devices and present three comprehensive application examples: nanofluidically tunable photonic crystals, optofluidic microscopy and DFB dye lasers.

In this report, we review our recent results in the optical micromanipulation of vesicles. Traditionally, vesicle manipulation has been possible by employing photon momentum and optical trapping, giving rise to unique observations of vesicle shape changes and soft matter mechanics. Contrary to these attempts, we employ photon energy rather than momentum, by sensitizing vesicles with an oxidizing moiety. The later converts incident photons to reactive oxygen species, which in turn attack and compromise the stability of the vesicle membrane. Both coherent and incoherent radiation was employed. Polymersome re-organization into smaller diameter vesicles was possible by focusing the excitation beam in the vicinity of the polymersomes. Extended vesicle illumination with a collimated beam lead to their complete destabilization and micelle formation. Single particle analysis revealed that payload release takes place within seconds of illumination in an explosive burst. We will discuss the destabilization and payload release kinetics, as revealed by high resolution microscopy at the single particle level, as well as potential applications in single cell biomodulation.

We demonstrate a digital phase conjugation technique for generating a sharp focus point at the end of a multimode optical fiber. A sharp focus is experimentally obtained at the distal end of a 200 mu m core multimode fiber. By recording the digital holograms for different excitation conditions, the sharp focus can be digitally scanned over a 175 mu m diameter regular grid. The demonstrated technique is used for high resolution scanning lensless imaging based on multimode fibers, of stained biological samples that can enable diagnosis from the investigation of cellular phenotype.

By employing anisotropic fluids and namely liquid crystals, fluid flow becomes an additional degree of freedom in designing optofluidic devices. In this paper, we demonstrate optofluidic liquid crystal devices based on the direct flow of nematic liquid crystals in microfluidic channels. Contrary to previous reports, in the present embodiment we employ the effective phase delay acquired by light travelling through flowing liquid crystal, without analysing the polarisation state of the transmitted light. With this method, we demonstrate the variation in the diffraction pattern of an array of microfluidic channels acting as a grating. We also discuss our recent activities in integrating mechanical oscillators for on-chip peristaltic pumping.

By replacing common buffers with anisotropic liquids in microfluidics, an enhanced range of optofluidic functionalities is enabled. Such an anisotropic liquid is nematic liquid crystals (NLC), which exhibits optical properties that can be tuned by optical, electrical or mechanical fields, such as flow. We demonstrate an optofluidic modulator based on direct flow of nematic liquid crystals in microfluidic channels. We discuss this optofluidic paradigm both under steady state conditions, and under flow. Rapid pulsatile flows are detrimental towards more compact and ultra-fast devices. These were enabled via peristaltic pumps, demonstrating liquid crystal modulators operating above the limit of 3 kHz. We discuss the latter results, but also assess the feasibility of performing ultra-fast optics and additional functionalities for on- and off-chip imaging.

Surfaces -defined as the interfaces between solids and liquids- have attracted much attention in optics and biology, such as total internal reflection imaging (TIRF) and DNA microarrays. Within the context of optofluidics however, surfaces have received little attention. In this paper, we describe how surfaces can define or enhance optofluidic function. More specifically we discuss chemical interfaces that control the orientation of liquid crystals and the stretching of individual nucleic acids, diffractive and plasmonic nanostructures for lasing and opto-thermal control, as well as microstructures that read pressure and form chemical patterns. © 2010 SPIE.

We present a pressured mediated tunable optofluidic dye laser with novel cavity. The dye laser chip was fabricated with Polydimethylsiloxane (PDMS) via replica molding and has none nano-features. It comprises a liquid waveguide and micro-scale air-gap chambers which function as mirrors to provide feedback. The lasing wavelength was determined by the interference of the reflected beams from the two PDMS-air interfaces of the air-gap chamber acting as Fabry-Perot etalon, while the tuning was realized by varying the width of the air-gap by applying air pressure. The lasing with linewidth of 3 nm and tuning range of 14 nm was demonstrated. © 2010 Copyright SPIE - The International Society for Optical Engineering.

By integrating soft-lithography-based nanofluidics with silicon nanophotonics, we demonstrate dynamic, liquid-based addressing and high Δn/n(∼0.1) refractive index modulation of individual features within photonic structures at subwavelength length scales. We show ultracompact tunable spectral filtering through nanofluidic targeting of a single row of holes within a planar photonic crystal. We accomplished this with an optofluidic integration architecture comprising a nanophotonic layer, a nanofluidic delivery structure, and a microfluidic control engine. Variants of this technique could enable dynamic reconfiguration of photonic circuits, selective introduction of optical nonlinearities, or delivery of single molecules into resonant cavities for biodetection. © 2006 Optical Society of America.

We present a holographic recording technique with 150 femtosecond time resolution. This technique allows us to capture either a single hologram with fine spatial resolution (4 micrometers), or a time-sequence of multiple holograms with reduced spatial resolution in a single-shot experiment, while preserving amplitude and phase information. The time resolution and the frame rate are limited only by the duration of the laser pulses. The holograms are recorded on a CCD camera and digitally reconstructed. We have used the technique to study the nonlinear propagation of high energy femtosecond pulses through liquids. We have observed dramatic differences in the pulse propagation characteristics depending on the strength of the nonlinear coefficient of the material and it's time response. The fine spatial resolution allows us to zoom in and visualize the spatial profile of the pulses breaking up into multiple filaments while the phase recovered from the holograms helps us identify the nonlinear index changes in the material. We have measured both positive and negative index changes. Very fast positive index changes are generally attributable to the Kerr nonlinearity. The negative index changes can be caused by electron plasma generated by multiphoton absorption.

We present two applications of volume holographic filters in the reflection geometry. A passive athermal holographic filter design is realized through the mutual compensation between the temperature coefficients of the bulk hologram and a variable incident angle controlled by a bimetallic cantilever. Seven holograms are multiplexed to constitute a multi-line filter which can be used to emulate specific absorption or emission spectra for spectroscopic applications.

In this paper we report on a holographic method used to record fast events in the nanosecond time scale. Several frames of the expansion of shock waves in air and in a polymer sample are recorded holographically in a single shot experiment, using a pulse train generated with a single pulse from a Q-switched Nd:YAG laser. The time resolution is limited by the laser pulse width, which is 5.9 ns. The different frames are recorded on the holographic material using angle multiplexing. Two cavities are used to generate the signal and reference pulses at different angles. We also present a method in which the recording material is replaced by a CCD camera. In this method the holograms are recorded directly on the CCD and digitally reconstructed. The holograms are recorded on a single frame of the CCD camera and then digitally separated and reconstructed.

In:holographic data storage, pages of information are overlapped in the volume of the recording medium. Due to destructive read-out of holograms in photorefractive crystals such as LiNbO3:Fe, holograms are recorded with an exposure schedule in order-to equalize diffraction efficiency. This leads to a final diffraction efficiency proportional to 1/M-2 where M is the number:of exposures. Coherent erasure of a particular page also erases all the other pages stored in the same volume. We believe to have found a technique that does not require an exposure schedule and that can record M holograms with diffraction efficiency following a 1/M dependance. Our technique is based on non-destructive read-out in doubly-doped LiNbO3 [1]. The technique is based on the recording of localized holograms in thin layers across the volume of the crystal.

The Optically Programmable Gate Array (OPGA), an optical version of a conventional FPGA, benefits from a direct parallel interface between an optical memory and a logic circuit. The OPGA utilizes a holographic memory accessed by an array of VCSELs to program its logic. An active pixel sensor array incorporated into the OPGA chip makes it possible to optically address the logic in a very short time allowing for rapid dynamic reconfiguration. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module can be made compact. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and database search.

The high data transfer rate achievable in page-oriented optical memories demands for parallel interfaces to logic circuits able to process efficiently the data. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification.

An experimental demonstration of a set of optical logic gates (OR, XOR, AND) is shown using non-linear mixing in a BBO crystal. Pulses generated by a femtosecond Ti:Sapphire laser at 800 nm (140 fs duration, 2nJ/pulse) are split in 4 beams evenly separated in space and propagating collinearly. The 4 beams are focused by a singlet lens in the non-linear crystal and frequency doubled using a type I non-colinear phase matching (e = o + o). Due to spherical aberrations of the lens, the 2 beams that are far from the optical axis are brought into a focus that is slightly further away from the focus formed by the 2 beams closer to the optical axis. The frequency-doubted light generated by the two foci propagates in the same direction. An OR gate is produced by constructive interference of the frequency doubled pulses. A XOR gate is produced using destructive interference. OR and XOR can be programmed from a single gate by adjusting time delays of the inputs. We raise the possibility of coating a cascaded set of gates for a femtosecond time scale computing system using photoinduced absorption in polyacetylene substitutes.

Reconfigurable processors bring a new computational paradigm where the processor modifies its structure to suit a given application, rather than having to modify the application to fit the device. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multipexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification.

Phenanthrenequinone (PQ)-doped poly(methyl methacrylate) (PMMA) is a photopolymer holographic recording material that can be made in large thicknesses and does not exhibit any shrinkage. Holograms are made permanent by a post-recording diffusion amplification process. PQ-doped PMMA thus exhibits many properties which make it an ideal candidate as a high-density read-only holographic data storage medium.

We present a novel method for recording persistent holograms in doubly-doped LiNbO_3. Simultaneous sensitization of the crystal by an inhomogeneous UV beam can result to 32% diffraction efficiency recorded by red light in a 0.85 mm thick sample, while read-out with only red light is non- destructive. Rapid optical erasure by ultraviolet light is possible and light scattering is efficiently prevented.

We present an efficient, non-volatile holographic storage scheme in doubly doped lithium niobate, with red recording light and simultaneous illumination by homogeneous ultraviolet light.

We have designed and implemented a compact holographic memory module that uses a dual spatial-light modulator/detector optoelectronic integrated circuit in the lens-less phase- conjugate geometry. In this paper we discuss optical design and systems issues and present recent experimental results. ©2004 Copyright SPIE - The International Society for Optical Engineering.

The demonstrate the storage of 1000 holograms in LiNbO3:Fe, recorded at 488nm and read at 633nm to reduce decay during read-out. We minimize Bragg mismatch problems of the two-wavelength scheme by using thin crystals, while combining peristrophic and angle multiplexing to counter the poorer angular selectivity of thin crystals. We find the reduction in read-out decay to be significant: but limited by dark conductivity.

We review methods of nonvolatile storage in photorefractive materials, namely thermal and electrical fixing, two-lambda readout, two photon recording, and periodic refreshing. For each method, we briefly review the physical processes that are responsible for counteracting photorefractive erasure, and present recent experimental results.

Keywords: shift multiplexing ; holographic 3D disks ; surface storage density Reference EPFL-CONF-158466View record in Web of Science Record created on 2010-11-25, modified on 2017-05-10

Keywords: Mems ; magnetic ; scanning mirror ; holographic memory Reference EPFL-CONF-158464View record in Web of Science Record created on 2010-11-25, modified on 2017-05-10

The various optical interconnection schemes that have been developed for the implementation of neural network architectures are reviewed. Volume holography in photorefra.ct.ive crystals is the most powerful interconnection method for this application. The use of liquid crystal smart pixel technology for the realization of the nonlinear activation function of the neurons is described. A novel method for combining liquid crystal devices and photorefractive holograms that leads to a very compact and versatile package, is presented.

We have achieved a surface density of 10 bits/µm^2 (6.5 Gbits/in^2) with an experimental holographic storage setup, using DuPont's 100 µm thick photopolymer as the recording medium. Its performance characteristics in terms of access rate and signal-to- noise-ratio are described. Furthermore, a simple holographic 3D disk system with high surface density (10 bits/µm^ using a 100 µm thick recording material) and an architecture similar to compact disks is shown.

Keywords: Holographic Storage ; Holographic 3D Disks ; Angle Multiplexing ; Peristrophic Multiplexing ; Shift Multiplexing ; Surface Storage Density Reference EPFL-CONF-158483View record in Web of Science Record created on 2010-11-25, modified on 2017-05-10

We describe a page—formatted random—access holographic memory capable of storing up to 160,000 holograms.A segmented mirror array allows a 2—dimensional angle scanner to provide access to any of the stored holograms.High—speed random access can be achieved with a non—mechanical angle scanner. We demonstrate holographicstorage and high—speed retrieval using an acousto—optic deflector (AOD). 1 INTRODUCTION In volume holographic memories data is stored in the interference patterns formed by coherent beams of light. The information is imprinted on one of these beams (object beam). Multiple pages of data can be superimposedwithin the same volume of a storage medium. These pages, stored as separate holograms, can be independently accessed by changing either the angle,' wavelength2'3 or phase code4'5 of the reference (non—information—bearing) beam. The storage capacity C achievable with each of these methods can be written as C = NM, where N is thenumber of bits in each stored page, and M is the number of pages superimposed in the same volume. Assumingone bit per pixel, current spatial light modulator (SLM) technology can provide 105_106 bits per stored page.Because these pixels are recalled in parallel by a single reference beam, very high data rates can be achieved.We describe a holographic data storage system in which the data rate is limited only by the material dynamicrange. By using the 90° interaction geometry, we have enough distinct reference angles for storage of 10,000holograms at a single location. A segmented mirror array enables non—mechanical scanners to provide high—

Keywords: Photodetectors ; Gaas Mesfets ; Fet-Seeds ; Optical Neural Networks ; Smart Pixels Reference EPFL-CONF-158488View record in Web of Science Record created on 2010-11-25, modified on 2017-05-10

We describe a page-formatted random-access holographic memory designed to store up to 160,000 holograms. The memory consists of 16 vertically spaced locations, each containing 10,000 holograms, which in turn are organized as 10 fractal-multiplexed rows of 1000 angularly-multiplexed holograms. A segmented mirror array is used to enable random access to any of the stored holograms within the access time of a non-mechanical angle scanner such as an acousto-optic deflector. Using a mechanical scanner with such a mirror array, we demonstrate storage of 10,000 holograms at a single location of the system, as well as simultaneous storage and recall of holograms at 6 locations, including the highest and lowest of the 16 locations.

The recording characteristics of DuPont's HRF-150 photopolymer film are described. The application of these films for data storage using the 3-D holographic disk architecture is presented. The required system's bandwidth due to the photopolymer's limited thickness is shown to be the limiting factor of the storage capacity of these thin films and not the material's dynamic range. A new multiplexing method (peristrophic multiplexing) that significantly increases the film's capacity and changes the limiting factor from system bandwidth to material dynamic range is presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The photorefractive and electrical properties of ferroelectric tungsten bronze (T.B.) materials are reviewed with respect to optical data storage applications. Our work indicates that both the photorefractive properties (speed and coupling) and dark conductivity are sensitive to the type of T.B. host, dopants, and structural defects. The filled-lattice T.B. crystals exhibit faster response and lower dark conductivities, which are needed for data storage applications, as compared to unfilled T.B. crystals. Concepts for 3-D holographic memory applications using these materials arc discussed.

Periodic copying and electrical fixing are presented as two practical methods for controlling the decay rate of volume photorefractive holograms in the implementation of optical image processing systems.

Angularly multiplexed transmission holograms were recorded at multiple spots on a photopolymer coated disk. By imaging in the `along track' direction and Fourier transforming in the radial direction when recording and presenting images, disk rotation can be used to generate the 2D correlation functions between stored templates and presented images. The correlation functions for holograms multiplexed at a given spot are generated line by line and detected in parallel. A theoretical model of operation was developed and experimentally verified.

In this paper we explore the use of 3D disks for the construction of networks with extremely large storage capacity. 3D disks can store up to 1012 weights per disk. In this paper we discuss how 3D disks are used to implement an optical neural network and then derive the capacity and speed of the resulting architecture.

We describe a two-layer neural network using holographic optical disks as the interconnection weights. Such a system can be used to implement one two-layer with large number of hidden units, or several two-layer networks with smaller number of hidden units.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A 3-D holographic optical memory is described that combines spatially and angularly multiplexed storage to yield a storage capacity of approximately 1012 bits in a crystal with volume less than 100 cm3. A non-mechanical scanning mechanism, consisting of acoustooptic deflectors and a segmented mirror, retrieves any stored hologram in a time equal to the acoustic delay through the aperture of the acoustooptic deflector.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe a two-layer neural network using holographic optical disks as the interconnection weights. Such a system can be used to implement one two-layer with a large number of hidden units, or several two-layer networks with a smaller number of hidden units© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe a photorefractive 3-D optical disk for data storage. The information is stored at several recording locations on the disk as angle-multiplexed holograms. Design parameters that affect alignment sensitivity and diffraction efficiency are considered.

In a holographic optical learning network, the decay of multiply exposed holographic interconnections can adversely affect the training of the network. A new dynamic photorefractive holographic memory is described that allows an arbitrarily long sequence of adaptations by rejuvenating decayed holograms with a simple all-optical feedback loop.

GaAs optoelectronic integrated circuits (OEICs) require the combination of several types of devices that place widely differing demands upon the layer structure and processing technologies. We report on the development of MESFETs, bipolar transistors, detectors, and a unique class of beam-steered facetless grating surface-emitting lasers, and the integration of up to 300 devices of multiple types.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The optical implementation of a neural network consists of two basic components: a 2-D array of neurons and interconnections. Each neuron is a nonlinear processing element that, in its simplest form, produces an output which is the thresholded version of the input. Liquid crystal spatial light modulators, optoelectronic integrated circuits (OEIC's), either hybrid, such as liquid crystal on silicon, Si-PLZT, and flip-chip devices, or monolithic integration in 111-V compounds, are examples of such a solution. In order for these devices to be used as neurons in a practical experiment, they must contain a large number of neurons (104/cm2 - 106/cm2) and exhibit high gain. This puts a stringent requirement on the electrical power dissipation. Thus, these devices have to be operated at low enough current levels so that the power dissipation on the chip does not exceed the heat-sinking capability, and yet the current levels need to be large enough to be able to produce high gain. This means sensitive input devices are a must. To achieve these goals, the speed requirement of the devices must be relaxed as the operation of neural network does not have to be too fast.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.