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International audience; This paper described a wavelength-selective couplers dedicated to drop functionality (spectral-selective couplers dedicated to wavelength demultiplexing). It is consist of two Y junctions: an input two drop channels and an output. The Y-branches distributors of optical power were carried out by a specific geometry of Ti:LiNbO3 waveguides. Each Y junction is composed by two identical bends jointed at one with a weak inclination angle to decrease losses. On each arm of the Y-branches, a Bragg grating (BG) is etched by Focused Ion Beam (FIB) in order to extract a specific wavelength band. A two-channel configuration is adopted which demonstrate a drop functionality of two spectral bands centered at 1123 nm and 1527 nm. The complementary spectrum is avalaible at the coupler output. Index Terms-Bragg reflectors, drop channels, wavelength filtering devices, Y-branch coupler.

Demonstration of coherence modulation of light is reported for the first time in the area of acousto-optic signal processing. The method allows electro-optic modulation of broadband sources to be used in acousto-optic time integrating correlators, with a modulation depth and a dynamic range comparable to those of coherent systems. Though a single coherence-modulated channel is used, it demonstrates that a generalization of the method to several channels is possible.

International audience; In this paper we have studied effect of depth etching on the Bragg gratings (BGs) realized by Focused Ions Beam. This technique has the advantage to induce a direct waveguide structuring without intermediate media, comparing to traditional methods. A reflectivity of 96% within a window centred at 1550 nm is obtained. The effect of the depth etching on the transmittance and the bandwidth at half maximum is demonstrated.

International audience; Optimised compression of femtosecond fibre laser pulses in highly nonlinear fibre is demonstrated. Specifically reported are compressed pulse durations below 30 fs using a simple setup where a single sub-10 cm segment of highly nonlinear fibre is directly spliced to the output pigtail of a commercial femtosecond fibre laser. The compressed pulse quality is confirmed through frequency resolved optical gating measurements.

We experimentally demonstrate parabolic pulse generation around 1550 nm in dispersion decreasing comb-like profiled fiber. Frequency resolved optical gating is used to confirm the output pulse parabolic intensity profile and linear chirp.

This paper describes a recording and reconstruction method applied to two-dimension Fourier holography, in which the illumination at the recording stage is spatially coherent and temporally incoherent. The various chromatic components of the information to be recorded in the hologram are spread along a direction orthogonal to the entrance slit of a spectroscope that behaves as scanning pupil performing a chromatic coding. The message, both spatially and temporally coded, can be reconstructed by using a conventional process, the light source being still polychromatic.

Many applications of zone plates illuminated in polychromatic light make use of the wavelength dependence of the focal length. Especially in the field of multichannel processing in polychromatic light or of surface topography by chromatic detection, the measurement of the spectral resolution of the zone plate is a very important parameter which determines setup performance. The authors deal with a theoretical study of such a spectral resolution. The analysis, based on Fresnel diffraction theory, gives the spectral bandwidth that can be resolved along the optical axis. Experimental measurements are in good accordance with the theoretical expected values: the spectral resolution depends on the zone plate characteristics; it also depends on the wavelength and on the diameter of the illumination beam. This dependence is important for zone plates with a low aperture but is negligible for large aperture.

Multiple interference fringes generated by a Fabry-Perot interferometer are used for realizing phase Fresnel lenses. The authors deal with a parallelism between the decomposition of a spherical wavefront in Fresnel zones and a multiple interference pattern obtained with a FP cavity with specially designed mirrors. In the first section, the authors show that the phase profile of a Fresnel lens can be described as the superposition of pseudo-sinusoidal functions whose amplitude and phase are given by a Fourier decomposition. Synthesis of the Fresnel lens profile can be carried out by multiple interference fringes formed by a FP cavity observed in reflection. The reflection coefficients of the mirrors of the cavity make the amplitude and the phase of multiple waves proportional to the Fourier terms. Experimental results are reported in the second section. Multiple fringe patterns are recorded on bleached holographic plates. The diffraction efficiency of Fresnel lenses thus obtained is 65%.

Diffraction of light by ultrasonic waves can be used to produce luminous images of acoustical transparencies. A geometrical interpretation of the imaging mechanism is proposed. The interaction phenomenon is first considered in a principal section plane: the optical image of an acoustical point source can be obtained. An object-image relationship is given. The extension that analysis to 3D interaction gives theoretical diffraction results: in space, the acousto-optic transformation is not an orthogonal one. Consequently, visualization of an image similar to the object requires the use of an anamorphote device. An experimental set-up is described and some experimental results are given as examples.

A specific configuration is proposed wherein two zone plates combined with an achromatic objective permits to cancel the chromatic scale factor as broad-band illumination is used in the Fraunhofer diffraction process. The set-up acts as a wavelength-independent Fourier transformer yielding an achromatic diffraction pattern of any complex pupil. Experimental results are also presented and demonstrate the ability of the system to work over the visible spectrum.

A conventional intra-cavity Pockels cell was used to achieve tunable operation of a Rh 6G dye laser. Wavelength tuning over a broad spectral band (500 PO with driving voltages of some hundreds volts was achieved. This system is suitable for simulating broadband illumination in optical processors working with spatially coherent but temporally incoherent sources. Applications dealing with the measurement of optical path-differences through the channelled spectrum technique, surface testing by chromatic speckle phenomenon and optical transmission by spectral modulation of light are reported.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

It is well‐known that the introduction of a path‐difference between two beams of white light likely to interfere corresponds to a sinusoidal filtering of the temporal frequencies of the light observable as a channelled spectrum. This property can be used in information transmission, the power spectrum of white light being then filtered. The device proposed here is based on the Pockels effect induced by an electric field in an electro‐optic crystal behaving as a two‐wave interferometer whose path‐difference is proportional to the electric field. As a result, a white light beam travelling through the crystal undergoes a chromatic filtering that encodes the electric signal. The decoding is carried out by spectral analysis of the light using either grating‐ or prism‐ spectroscope, or birefringent quartz plate acting as a Fourier Transform Spectroscope. The electro‐optic bandwidth is expected to range up to 100 Mhz. Preliminary experiments show that an optical fiber used as transmission line fits the whole range of the light frequencies, independently or any dispersion effects.

A review of the main landmarks which proceed the fundamentals of space‐time optics is given. It includes a comparison of the roles of space and time variables in optics as far as information transfer is concerned. Illustrations deal with interference and diffraction phenomena, the light beam being considered as a carrier whose capacity is linked to the width of the spectral band. Experimental examples are reported in metrology, information processing, spectral analysis and wavelength coding, holography, transmission by spectral modulation, etc.