Optical microscopy for measuring tapered fibers beyond the diffraction limit.

We describe a technique that allows the improvement of the resolution of optical microscopes for nanofiber measurements beyond the diffraction limit. It can be readily implemented on any microscope. We demonstrated it by measuring tapered fibers radii from 0.4 to 4 µm with a resolution below the diffraction limit, from a few nanometers up to 50 nm in the worst case, depending on the radii. This technique is a non-contact measurement with the microscope objective placed a few centimeters from the nanofiber. We acquire the experimental diffraction pattern by scanning the object plane of the microscope system, upstream and downstream the nanofiber. We compare this experimental diffraction pattern to a bank of all the simulated patterns for all the radii. The radius of the simulated diffraction pattern that best matches to the experimental one is the sought radius.

Efficient Raman converter in the yellow range with high spatial and spectral brightness.

We present a Raman converter emitting at 583 nm on the second Stokes order of a line of propan-2-ol pumped by a microlaser at 532 nm in the sub-nanosecond regime. We used a mixture of liquids to adapt the transmission band of a photonic bandgap fiber. The internal conversion efficiency is 67% in photon numbers, and the output power is 1.06 mW, corresponding to a maximum peak power of 338 W. The beam delivered by the converter presents a Gaussian spatial structure and a high spectral brightness, typically more than five times higher than supercontinuum sources in this spectral range.

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.

Design and implementation of a page-oriented "holographic" memory based on a Lippmann architecture.

Optical data storage inspired by Lippmann interference color photography was proposed a long time ago as an alternative to holographic memories. Very high capacities were predicted for a page-oriented approach with wavelength multiplexing, but, up to now, such an architecture has never been implemented. Based on simple conception rules, we build such a page-oriented Lippmann data storage system. Submicrometer resolved data pages recorded in thick materials are evidenced by the experimental results.

Balanced homodyne detection of Bragg microholograms in photopolymer for data storage.

Wavelength multiplexed holographic bit oriented memories are serious competitors for high capacity data storage systems. For data recording, two interfering beams are required whereas one of them should be blocked for readout in previously proposed systems. This makes the system complex. To circumvent this difficulty and make the device simpler, we validated an architecture for such memories in which the same two beams are used for recording and reading out. This balanced homodyne scheme is validated by recording holograms in a Lippmann architecture.

Continuous monitoring of a surface slope by real-time shearing interferometry with a photorefractive crystal.

We propose and demonstrate a new technique for measuring the temporal variations of the surface slope of an object. This real-time shearometric arrangement takes advantage of the dynamic properties of holograms in photorefractive crystals. The accuracy of the measurements should make this technique suitable for real-time structural intensity determinations.

Homodyne detection readout for bit-oriented holographic memories.

Homodyne detection is proposed to increase the readout signal of bit-oriented holographic memories. It can be easily implemented on present memory architectures by making the diffracted signal interfere with a reflection of the reading beam. The large resulting increase of the readout signal can be used to enhance the data transfer rate. A first experimental demonstration of such a readout procedure is presented.

Self-induced transverse mode selection in a photorefractive extended cavity laser diode.

Previous works on photorefractive self-organizing laser cavities were about lasers that oscillate, prior the self-organization process occurs, on a set of axial modes sharing the same transverse structure. In a well-designed broad-area laser diode extended cavity, we theoretically and experimentally demonstrate that the insertion of a photorefractive crystal can also affect the transverse modal structure to force the laser, initially oscillating on several transverse modes, to oscillate on a single transverse and axial mode. This spatial self-organization process leads to an enhancement of the single mode operating range of the laser.

Relaxation of the single-mode emission conditions in extended-cavity semiconductor lasers with a self-organizing photorefractive filter.

Commercial 1.55-microm extended-cavity semiconductor lasers provide single-mode operation that can be continuously tuned over a range larger than 100 nm without mode hopping. But such performance requires delicate factory adjustment and high mechanical stability of the external cavity. Furthermore, at high emission power the tuning range is limited to small values because of the annoying multimode operations that sometimes occur. We have shown that the alignment constraints can be relaxed by use of an intracavity photorefractive filter. Here we present new results obtained with a crystal with low absorption and high photorefractive gain. We demonstrate that, without inducing excessive additional loss, we can preserve single-mode emission at an output power higher than the maximum power obtained in the absence of a photorefractive crystal over the full tuning range of the laser.