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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; The novel propagation characteristics of Bessel beams have been widely applied to optical manipulation and harmonic generation, and have provided new perspectives on fundamentals of ultrashort laser pulse propagation in nonlinear media. Fully exploiting their many unique properties, however, requires the development of techniques for the generation of high quality Bessel beams with flexible adjustment of the beam parameters. Moreover, long working distances are needed to produce Bessel beams inside bulk samples. In this paper, we report on the development of a novel spatial light modulator based setup that combines the properties of parameter flexibility, long working distance, high throughput and operation on micron-scale. We report both on the general characterization of the beam properties as well as a specific application in surface nanoprocessing.

The authors describe the principle of operation and the performance of a newly integrated LiNbO/sub 3/ modulator specially designed to generate optical delays of several millimeters. This is achieved by using the simultaneous propagation of the TE and TM modes in a waveguide and by taking benefit of the high natural birefringence of LiNbO/sub 3/. This modulator is well-suited to coherence modulation of light in fiber-optic transmissions. When powered by a short coherence source, the large optical delays induced by a cascade of such modulators can be used as information carriers to transmit several signals simultaneously. A demonstration is reported using a single source and two modulators in cascade to transmit signals simultaneously. >

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.

We describe a method suitable for the measurement of phase mismatch in a LiNbO3 Z-propagating TE-TM convertor. The method is based on the measurement of the transmission peaks produced by a mode coupling voltage applied to the electrodes. A major advantage of the method is that it allows phase mismatch measurements to be performed with quite a few parameters easily assessable experimentally (operating wavelength and electrode length).

A polarization-independent transmission link on a single mode fiber at 1300-nm wavelength is demonstrated using coherence multiplexing. The use of a source with a very short coherence length (about 200 mu m) allows an easy implementation of the suitable optical delays (some millimeters) using LiNbO/sub 3/ modulators matched to fiber interferometers. Experiments were conducted with transmission of analog signals and baseband TV signals on a 2500-m-long single mode fiber. The polarization-independence of the method is obtained at the cost of relatively high losses. The high losses are introduced by the interferometers that are required at both ends of the link (theoretical losses of -3 dB/interferometer). They are physically inherent in the coding and detection process, which requires optical delays greater than the coherence length, and hence cannot be decreased. >

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 reports a novel optoelectronic nonlinear oscillator, which produces a chaotically phase-modulated light beam over a bandwidth greater than 5 GHz. The setup is intended for high-speed chaos-based secure communications. The nonlinear process is performed by the transient response of a fiber interferometer. The flexibility in the definition of such an all-optical nonlinearity features a potentially high-dimensional key space of the encryption process. Modeling, simulations, and experimental results of the dynamical behaviors are reported.

The coupling ratio of directional couplers in Z-cut Y-propagation and X-cut Z-propagation LiNbO 3 crystals was adjusted by laser ablation. The coupling ratio change is more efficient for the TM-mode of Z-cut couplers. The method can be used to correct the uncertainty of the coupling ratio for directional couplers that occurs during fabrication process.

In this paper, we report theoretical and experimental results concerning the upconversion phenomena around 550 nm in Er 3+ -doped Ti:LiNbO 3 waveguides. This phenomena corresponds transitions between the levels 4 S 3/2 implied by 4 I 15/2 . The waveguide is pumped near 980 nm with a laser diode. Two pump photons are used to bring the Er ions to the short lifetime level 4 F 7/2 . After a non-radiative transition to the level 4 S 3/2 , Er ions emit photons at 550 nm while falling down to the 4 I 15/2 level. By using the theoretical model elaborated by McCumber we evaluate the homogeneous emission cross sections and we obtain the following maximum values of the cross sections (sigma) H e (551.9 nm) equals 57.7 x 10 -26 m 2 for TE and (sigma) H e (558.1 nm) equals 52.5 x 10 -26 m 2 for TM polarizations. By measuring the fluorescence radiation around (lambda) equals 550 nm, we determine the rising and falling times and we obtain C equals 0.198 x 10 -23 m 3 /s as the value of the modulus of the homogeneous upconversion factor the value. The results presented here can be used in the design of integrated optoelectronic circuits and in the modeling of the laser action and optical amplification in Er 3+ -doped Ti:LiNbO 3 waveguides when a 980 nm pumping is considered.

In this paper we demonstrate up-conversion emission at 550 nm into an Er-doped Ti:LiNbO 3 waveguide pumped by a 980 nm laser diode. The two main processes of the up-conversion are the sequential two photon absorption (STPA) and the energy transfer (ET). In our case, the fluorescence lifetime of the 4 S 3/2 energy level of the Er 3+ ion is measured as 32 microseconds. The fluorescence spectrum shows two peaks around 550 nm and 558 nm which are strongly polarization dependent. This effect is attributed to the different crystal fields induced by the location of Er 3+ ions in the different LiNbO 3 crystal lattices. The variations of the fluorescence intensity and the transmitted pump power are studied versus the length of Er-doped waveguide. The fluorescence intensity has a quadratic behavior versus the coupled pump power which demonstrate that the up-conversion mechanism is mainly due to a STPA process.

Absolute measurement ofthe fiber to waveguide distance during a coupling process by low-coherence interferometiyHenri Porte, Wilhelm Efflein, Richard FerriereLaboratoire d'Optique P.M.Duffieux, TJRA CNRS 214, UIFR Sciences et TechniquesUniversite de Franche Comte, 16, route de Gray, F-25030 Besancon cedex, FranceABSTRACTDuring a fiber-to-waveguide connection process, it can be important to determine accurately the absolute distancebetween the end ofthe fiber and the edge ofthe optical waveguide without visual control. We investigate here the use of alow-coherence optical source whose light, transmitted by the fiber, is launched into the waveguide in order to control thealigmnent. The end faces ofthe waveguide and ofthe fiber form a Fabiy-Perot cavity for the transmitted light beam. Theoptical transmission versus the distance exhibits a fringe pattern whose visibility is related to the coherence properties of thebroadband source. We deduce the absolute distance from visibility measurements, we assess the accuracy ofthe method, andthe results are compared with the direct distance measurements.1. iNTRODUCTIONThe problem ofthe coupling ofan optical fiber to an optical waveguide for packaging has been investigated since thebeginning ofthe research in the field of integrated optics. Nevertheless, few simple, automatic and low-cost solutionsappeared, slowing down the development ofthe integrated optic devices and systems, which find the widest applications inthe field ofoptical telecommunications networks (switching, routing, multi/demultiplexing, modulation).In the frame ofa project dealing with the development ofan automatic positioning and alignment system, one of theproblems met consists in achieving the final contact between the fiber and the waveguide once the optical transmission isoptimized in the transverse plane [X,Y] and electronically locked on the maximum oftransmitted light. Without any visualcontrol, the system will steer the motion ofthe fiber to the waveguide and will stop the shifting when contact occurs. Thisrequires the accurate knowledge ofthe absolute value ofthe gap between the two devices before moving any of it, for instancethe fiber.The approach can be done by using a motorized set-up or using piezoelectric transducers. The accuracy of thedisplacement should be about 0. 1tm. As in available commercial systems, one can imagine to stop the advance along the Z-axis as soon as the optical transmission becomes constant and maximum, after a progressive increasing. However, thismethod brings with it the risks to, either, damage the edge ofthe waveguide, for instance in the case offragile ciystallinesubstrates, or more often, the risk to modify the position of the waveguide in the transverse plane [X,Y] .

A polarisation-independent integrated X-cut Z-propagating Er-doped Ti:LiNbO3 waveguide amplifier, pumped by a 980 nm laser diode, is reported for the first time. An amplifying gain of 0.95 dB/cm was achieved for only 40 mW of coupled pump power. The cross-section for α-polarisation and the losses are measured directly within the waveguide to check the accordance of the experimental amplification gain with the theoretical models published previously.

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.

Unlike conventional modulation techniques which generally require strict conditions upon the wavelength of illumination, the proposed electro-optic technique allows the transmission of a message with a broadband source. The principle of coding is based on an electro-optic phase modulation of light. Feasibility of the technique is demonstrated experimentally in white light in the case of the simultaneous transmission of two TV channels. Future prospects deal with multiplex transmissions. The technique might allow benefit to be taken of the broad spectral bands of LEDS that are widely used in wavelength multiplex systems.

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.

The authors report a wavelength independent TE-TM mode convertor used as a waveguide electrooptic modulator in a coherence modulated system. The modulation voltages thus obtained (20 V) are about 10 times lower than those previously reported in earlier coherence modulated devices. The modulator is a strip waveguide fabricated on Y-cut Z-propagation, Ti-indiffused LiNbO/sub 3/. When used in conjunction with a birefringent plate and polarizers, the modulator is shown to imprint on light a signal encoded into an optical delay greater than the source coherence length. Demonstration of the device is reported using a highly multimode laser diode at 820 nm. >

Pulse propagation in a vacuum is described as being the superposition of elementary pulses given by the time derivative of the initial pulse and weighted by local inclination factors attached to the pulse wave front. Optical pulses with any wave-front profile and propagating in near-field and far-field regions are considered. The analytical expressions thus obtained demonstrate the possibility to compute the pulse structure as a function of time and its evolution through numerical simulations.

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.

The use of an integrated TE-TM mode converter as a coherence multiplexer is described. The component is based on a buried waveguide obtained by proton exchange and postannealing. The electrode structure consists of three electrodes. Two are used to achieve TE-TM conversion, and the third is used to perform phase matching to ensure a high conversion efficiency. >

The behaviour of sound imaging systems by diffraction of light is analysed for the Raman-Nath diffraction region. The study is based on a geometrical interpretation of the phenomenon. Imaging relationships are established for plane objects and extended to the 3-D case.

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.

An achromatized Fourier processor working with spatially coherent but temporally incoherent light is described. A specific configuration is proposed wherein two zones plates combined with an achromatic objective permits to cancel the chromatic scale factor as broad-band illuminaaon is used in the diffraction process. Experimental results demonstrate the ability of the system to work over the visible spectrum.© (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.

A description of diffraction phenomena of a white light beam passing through a complex pupil, i.e., corresponding to a very irregular wavefront profile, demands the use of a local obliquity factor. The general form of the resulting signals is derived from the Kirchhoff integral. It depends on the transit time, and its evolution law, here studied with one transverse and with one longitudinal coordinates, can be extended to x, y, z, t. An illustratiion is given in the field of rough surface testing.

An achromatic Fourier transformer working with spatially coherent but temporally incoherent light is described both theoretically and experimentally. The achromatic Fraunhofer diffraction pattern results from the incoherent superposition of the monochromatic diffraction patterns generated by every spectral component of light. Wavelength compensation is achieved by a specific configuration combining airspaced zone plates and lenses. Several parameters, such as the spectral resolution of the setup or the spectral broadness of the source, govern the accuracy of coincidence of the various monochromatic patterns. Experimental results demonstrate the broadband operation of the system; the error on the achromatic Fourier transformation is 2% over the visible spectrum. Applications in colored image processing are also reported.