Holographic memory with localized recording

We experimentally demonstrate and characterize a memory module that features selective page erasure and readout persistence using the localized recording method in doubly doped LiNbO3. Pages of information can be selectively erased without partially erasing the whole memory. Data pages can be written over erased pages multiple times. Information is read millions of times before refreshing is required. We quantify the optical quality of the holograms by measuring their signal-to-noise ratio for a memory size up to 100 holograms. A compact phase-conjugate readout architecture is also presented and experimentally demonstrated

Localized holographic recording in doubly doped lithium niobate

Persistent holograms are recorded locally with red light in a LiNbO>3 crystal doped with Mg and Fe. Selective erasure is realized by use of a focused UV sensitizing light. We demonstrate the recording of 50 localized images as well as selective erasure in a 4 mm × 4 mm × 4 mm crystal. A comparison of the total recording time for M holograms obtained with the conventional distributed-volume recording and the localized methods is presented

Two-photon imaging through a multimode fiber

In this work we demonstrate 3D imaging using two-photon excitation through a 20 cm long multimode optical fiber (MMF) of 350 micrometers diameter. The imaging principle is similar to single photon fluorescence through a MMF, except that a focused femtosecond pulse is delivered and scanned over the sample. In our approach, focusing and scanning through the fiber is accomplished by digital phase conjugation using mode selection by time gating with an ultra-fast reference pulse. The excited two-photon emission is collected through the same fiber. We demonstrate depth sectioning by scanning the focused pulse in a 3D volume over a sample consisting of fluorescent beads suspended in a polymer. The achieved resolution is 1 micrometer laterally and 15 micrometers axially. Scanning is performed over an 80x80 micrometers field of view. To our knowledge, this is the first demonstration of high-resolution three-dimensional imaging using two-photon fluorescence through a multimode fiber

Folded shift multiplexing

Shift multiplexing is a holographic recording method that uses a spherical reference wave. We extend the principle to a thin slab of holographic material that acts as a waveguide. Total internal reflection folds the reference spherical beam in one dimension. We demonstrate that the shift selectivity with the folded spherical beam is independent of the slab thickness but depends instead on the numerical aperture of the coupled spherical wave. A shift selectivity of 0.5 µm has been achieved with a 1-mm-thick LiNbO3 crystal and 50 high-definition data pages are recorded with this method

Increasing the imaging capabilities of multimode fibers by exploiting the properties of highly scattering media

We present a novel design that exploits the focusing properties of scattering media to increase the resolution and the working distance of multimode fiber based imaging devices. Placing a highly scattering medium in front of the distal tip of the multimode fiber enables the formation of smaller sized foci at increased working distances away from the fiber tip. We perform a parametric study of the effect of the working distance and the separation between the fiber and the scattering medium on the focus size. We experimentally demonstrate submicron focused spots as far away as 800{\mu}m with 532nm light.Comment: 4 pages, 3 figure

Diffraction efficiency of localized holograms in doubly doped LiNbO3 crystals

The diffraction efficiency of M holograms superimposed in the volume of the recording medium is proportional to 1/M^2. We present a method, based on nondestructive localized holograms in a doubly doped LiNbO3 crystal, that allows us to also record M holograms in the same volume without an exposure schedule or a diffraction efficiency that has 1/M dependence. We compare experimentally the final diffraction efficiency obtained with the localized and distributed recording methods

Spatiotemporal self-similar fiber laser

In this Letter, we demonstrate, to the best of our knowledge, the first spatiotemporally mode-locked fiber laser with self-similar pulse evolution. The multimode fiber oscillator generates parabolic amplifier similaritons at 1030 nm with 90 mW average power, 2.3 ps duration, and 37.9 MHz repetition rate. Remarkably, we observe experimentally a near-Gaussian beam quality (M^2<1.4) at the output of the highly multimode fiber. The output pulses are compressed to 192 fs via an external grating compressor. Numerical simulations are performed to investigate the cavity dynamics which confirm experimental observations of self-similar pulse propagation. The reported results open a new direction to investigate new types of pulse besides beam shaping and nonlinear dynamics in spatiotemporal mode-locked fiber lasers.Comment: 8 pages, 5 figure

3-D measurements using conoscopy and application to ophthalmology

In this paper we present a novel method to measure 3-D quasi planar or quasi spherical reflective surfaces with submicron depth accuracy. Two implementations are presented: a scanning and a non-scanning system. The non-scanning device allows fast measurements and can be applied for eye-shape measurements. The paper is organized as follows: in the introductory section, we first demonstrate the principle of the conoscopic effect leading to the formation of the interferogram. The second and third sections explain respectively. the scanning and non-scanning methods based on the conoscopic effect. We present the experimental results from a simple measurement and show how they conform with theory

Optical-resolution photoacoustic imaging through thick tissue with a thin capillary as a dual optical-in acoustic-out waveguide

We demonstrate the ability to guide high-frequency photoacoustic waves through thick tissue with a water-filled silica-capillary (150 \mu m inner diameter and 30 mm long). An optical-resolution photoacoustic image of a 30 \mu m diameter absorbing nylon thread was obtained by guiding the acoustic waves in the capillary through a 3 cm thick fat layer. The transmission loss through the capillary was about -20 dB, much lower than the -120 dB acoustic attenuation through the fat layer. The overwhelming acoustic attenuation of high-frequency acoustic waves by biological tissue can therefore be avoided by the use of a small footprint capillary acoustic waveguide for remote detection. We finally demonstrate that the capillary can be used as a dual optical-in acoustic-out waveguide, paving the way for the development of minimally invasive optical-resolution photoacoustic endoscopes free of any acoustic or optical elements at their imaging tip

Three-dimensional microfabrication through a multimode optical fiber

Additive manufacturing, also known as 3D printing, is an advanced manufacturing technique that allows the fabrication of arbitrary macroscopic and microscopic objects. All 3D printing systems require large optical elements or nozzles in proximity to the built structure. This prevents their use in applications in which there is no direct access to the area where the objects have to be printed. Here, we demonstrate three-dimensional microfabrication based on two-photon polymerization (TPP) with sub diffraction-limited resolution through an ultra-thin, 50 mm long printing nozzle of 560 micrometers in diameter. Using wavefront shaping, femtosecond infrared pulses are focused and scanned through a multimode optical fiber (MMF) inside a photoresist that polymerizes via two-photon absorption. We show the construction of arbitrary 3D structures of 500 nm resolution on the other side of the fiber. To our knowledge, this is the first demonstration of microfabrication through a multimode optical fiber. Our work represents a new area which we refer to as endofabrication