Gilles Pauliat

Volume hologram multiplexing using a deterministic phase encoding method

Abstract We present a novel phase encoding method for high capacity optical data storage in volume photorefractive materials. Using deterministic orthogonal phase codes in a reference-based multiplexing technique, we obtain a system that is able to retrieve multiple images with high diffraction efficiency without energy losses, adjustment problems or any time delay. The number of images which can be stored with that method is theoretically calculated and it is shown that image retrieval without any crosstalk is possible. Moreover, the method is experimentally demonstrated for a set of four orthogonal phase addresses. Actual limitations of the system are finally discussed.

Potentialities and limitations of hologram multiplexing by using the phase-encoding technique.

The advantages and limitations of data storage in holographic materials by implementing a pure phase-encoding method of the reference beam are studied. We show that if deterministic orthogonal binary phase addresses are used, such a system is theoretically able to store as many images as the usual angular multiplexing method. However, we demonstrate that imperfections of available optical components generate optical noise and limit the storage capacity. We propose an improved recording technique to overcome some of these limitations.

Brillouin light scattering from surface acoustic waves in a subwavelength-diameter optical fibre

Brillouin scattering in optical fibres is a fundamental interaction between light and sound with important implications ranging from optical sensors to slow and fast light. In usual optical fibres, light both excites and feels shear and longitudinal bulk elastic waves, giving rise to forward-guided acoustic wave Brillouin scattering and backward-stimulated Brillouin scattering. In a subwavelength-diameter optical fibre, the situation changes dramatically, as we here report with the first experimental observation of Brillouin light scattering from surface acoustic waves. These Rayleigh-type surface waves travel the wire surface at a specific velocity of 3,400 m s−1 and backscatter the light with a Doppler shift of about 6 GHz. As these acoustic resonances are sensitive to surface defects or features, surface acoustic wave Brillouin scattering opens new opportunities for various sensing applications, but also in other domains such as microwave photonics and nonlinear plasmonics.

Dynamic holographic memory showing readout, refreshing, and updating capabilities.

We propose a new refreshing procedure for reading out a dynamic holographic memory without loss of information. The retrieved images are fed back to the memory after being thresholded and amplified. Experimental demonstration is performed with a LiNbO(3) photorefractive crystal.

Influence of piezoelectricity on the photorefractive effect

We demonstrate that the spatially modulated electric field that is associated with a photorefractive grating generates stress and strain components with symmetries that are different from those induced by a uniform electric field. Therefore, because of piezoelectricity and the elasto-optic effect, the symmetries of the effective dielectric and electro-optic constants to be used to describe the photorefractive effect differ from the symmetries of the usual dielectric and electro-optic tensors. We derive analytical expressions to be used to compute these new constants from the measured clamped and unclamped dielectric and electro-optic coefficients. Experimental evidence is presented.

Design and Simulation of Next-Generation High-Power, High-Brightness Laser Diodes

High-brightness laser diode technology is progressing rapidly in response to competitive and evolving markets. The large volume resonators required for high-power, high-brightness operation makes their beam parameters and brightness sensitive to thermal- and carrier-induced lensing and also to multimode operation. Power and beam quality are no longer the only concerns for the design of high-brightness lasers. The increased demand for these technologies is accompanied by new performance requirements, including a wider range of wavelengths, direct electrical modulation, spectral purity and stability, and phase-locking techniques for coherent beam combining. This paper explores some of the next-generation technologies being pursued, while illustrating the growing importance of simulation and design tools. The paper begins by investigating the brightness limitations of broad-area laser diodes, including the use of asymmetric feedback to improve the modal discrimination. Next, tapered lasers are considered, with an emphasis on emerging device technologies for applications requiring electrical modulation and high spectral brightness.

Dynamic phase-encoding storage of 64 images in a BaTiO3 photorefractive crystal.

Storage of 64 images (128 × 128 pixels) by the deterministic phase-encoding technique in a holographic memory is reported. A ferroelectric phase modulator permits a fast random image reconstruction (150 μs/image). Sources of cross talk arising from the imperfections of the optical components are studied and evaluated.

Determinations of the photorefractive parameters of Bi12GeO20 crystals using transient grating analysis

Abstract A method to characterize the photorefractive parameters of Bi 12 GeO 20 crystal is described. An analysis of the transient photoinduced grating under an external applied electric field allows to determine both the diffusion length and the Debyes screening length which are the important parameters for device applications.

Dynamic beam deflection using photorefractive gratings in Bi 12 SiO 20 crystals

New configurations for spatial beam steering of a near-infrared laser beam are presented. They are based on the interaction of the beam from a semiconductor laser with a dynamic grating photoinduced in a photorefractive crystal such as Bi12SiO20 (BSO). The demonstrated large values of the deflection angles (12°) result from a change in both the grating period and the orientation achieved by optical means. The Bragg condition over this large scan angle is maintained by either recording the grating with a variable wavelength (dye laser) or taking advantage of the spatial nonlinearities of the photorefractive effect. The respective advantages of these two techniques are discussed. Possible application to interconnection between optical fibers for broadband communication is considered.

Real-time double exposure holographic phase shifting interferometer using a photorefractive crystal

Abstract We present a double exposure interferometer using a Bi12GeO20 crystal as the holographic medium. Once the system is calibrated, the simultaneous acquisition of two phase shifted interferograms allows the real-time quantitative measurement of displacements of a scattering object. Experiments are conducted first with a chopped CW argon laser at 514 nm and second with 694 nm nanosecond pulses from a ruby laser. At 514 nm the accuracy is λ 29 ; it reduces to λ 15 at 694 nm.