E. Toussaere

Polarization insensitive electro-optic polymer modulator

Electro-optic waveguiding polymer devices are very attractive for optical communication systems as a result of simple and potentially low-cost fabrication procedures. Several functions, such as high speed modulation or switching, have been already demonstrated. However, their polarization sensitive response precludes any actual use in optical telecommunication systems. The traditional uniform poling procedure, a prerequisite processing step for electro-optic polymer based devices whereby an electric field is applied at the vicinity of the glass transition temperature resulting in statistical polar orientation of the chromophores, is responsible for polarization sensitivity. By way of different coplanar or sandwich electrode configurations, any desired prerequisite modulation axis can, however, be imprinted onto the material resulting in the possibility of balanced TE/TM polarization efficiencies. Monolithic integration of both electrode configurations within a Mach–Zehnder modulator is shown to result in ...

Refractive Index Changes in Polymers Induced by Deep UV Irradiation and Subsequent Gas Phase Modification

Poly(4-vinylbenzyl thiocyanate) (PVBT) and a copolymer of styrene and 4-vinylbenzyl thiocyanate (PST-co-VBT) were investigated with regard to changes of the refractive index under UV irradiation (λ = 254 nm). After irradiation, the refractive index n D of PVBT films increased from 1.629 to 1.660. In the case of the copolymer PST-co-VBT n D increased from 1.616 to 1.630. The change of the refractive index mainly resulted from the photoinduced isomerization of thiocyanate groups (SCN) to the corresponding isothiocyanates (NCS). The NCS groups formed in the irradiated zones were selectively modified with gaseous amines (ammonia, propylamnie, ethylenediamine, and hydrazine) to give thiourea derivatives vias an addition reaction. The gas phase modification induced further changes of the refractive index without any loss of the film quality (e.g. propylamine, Δn up to -0.026, an hydrazine, Δn up to +0.035). In addition, the thickness h of the polymer films increased by up to 21% as a result of the gas phase modification. In contrast, wet chemical treatment with bulky amines (1-methylnaphthyl-amine, 1-pyrenemthylamine) caused a considerable deterioration of the film quality. The variation of the refractive index in polymers such as PVBT and PST-co-VBT is of potential interest for holographic and the recordings and the setup of polymer based DFB lasers.

Polymer microring lasers with longitudinal optical pumping

We propose an optical pumping scheme for microring cavity lasers. The pump beam is end-fire coupled into the optical fiber that supports the microring cavity. When propagating along the fiber, the pump light is coupled into and excites the gain medium in the microring. We have demonstrated that this pumping geometry leads to an enhanced slope efficiency and significant reduction of the lasing threshold. In addition, as the excitation of the gain medium is uniform, certain effects that are prone to occur in the usual transversal pumping configuration because of nonuniform excitation can be avoided.

Photo-induced non-linear susceptibility patterns in electro-optic polymers

We present microscopic scale photo-induced non-linear susceptibility patterns in organic materials. This patterns are observed by reflection second harmonic generation microscopy and atomic force microscopy. The characteristics of the non-linear susceptibility tensor are engineered during the active film preparation. Several techniques have been used to pattern the non-linear response: re-alignment through a chrome mask of previously electrically poled samples, Lloyd-mirror interferometric configuration to imprint any desired susceptibility periodicity in the sample and all optical poling using mutually coherent beams from a frequency-doubled picosecond Nd:Yag laser. Images of different scanned patterns are shown, direct evidence of periodic structures, two-dimensional patterns and applications to 2D photonic crystals are discussed.

Direct evidence of open ray orbits in a square two-dimensional resonator of dye-doped polymers

Lasing has been observed in optically pumped 4-dicyanomethylene-2-methyl-6-( p-dimethylaminostyrl)-4H-pyran-doped poly(methyl methacrylate) square-shaped micropillars that allow four-bounce closed and open ray orbits with internal incident angle theta(inc) > theta(c) (the critical angle for total internal reflection) and with the associated surface waves that emit at the four corners. We also detect strongly TE-polarized and spatially varying emission from the square sidewalls that is due to leaky open ray orbits with theta(inc) near but less than theta(c) for two of the four bounces. By selectively pumping the square microcavity with a stripe-shaped beam, we excite different four-bounce ray orbits.

Polymer based polarization insensitive amplitude modulator: conception, technology and demonstration

Abstract Electrooptic (EO) waveguiding polymer devices are very attractive for optical communication systems by virtue of their simple and potentially low-cost fabrication procedures. Several functions such as high speed modulation or switching, have been already demonstrated. However, their so-far polarization dependant response precludes any actual use in optical telecommunication systems. The traditional uniform poling procedure, a prerequisite processing step for electrooptic polymer based devices whereby an electric field is applied at the vicinity of the glass transition temperature, results in uniform statistical polar orientation of the chromophores, and is, therefore, responsible for polarization sensitivity. By means of different coplanar or sandwich electrode configurations, any desired prerequisite modulation axis can, however, be imprinted onto the material, thus resulting in the possibility of balanced TE/TM polarization efficiencies. Monolithic integration of both electrode configurations within a Mach–Zehnder (MZ) modulator is shown to result in an original polarization insensitive electrooptic polymer amplitude modulator for integrated optics. Design procedures including modeling, fabrication as well as performance testing of the integrated sandwich and transverse electrode configurations device are discussed. Cladding is selected in view of ensuring both efficient poling conditions and maximal overlap of the modulation field with the active layer cross-section. Corresponding optimizations are presented for both electrode configurations.

Polymer-based microcavity with photoencoded quadratic nonlinearity.

Functional electro-optic polymer thin films embedded in microcavity structures have been poled by an all-optical procedure based on the interference of multiphoton absorption processes. The photoinduced X((2)) tensor was then further addressed at modal resonance for the fundamental wavelength, leading to significant enhancement of the second-harmonic-generation efficiency. An order-of-magnitude enhancement, which is due to electric field resonant conditions inside the microcavity, has been probed by an optical parametric oscillator, in comparison with a single-path thin-film configuration. This configuration opens new perspectives in the realm of nonlinear photonic device processing.

Enhanced photoinduced birefringence in polymer microcavities

We investigate photoinduced birefringence in functionalized polymer microcavities illuminated by a visible polarized cw laser beam. The cavity studied in this experiment consists of an assembly of two Bragg mirrors embedding a polymer film with tethered azobenzene dyes. Linearly polarized light induces orientationally selective excitation of the chromophore guests, resulting in optical anisotropy of the film. The mechanism of the phenomenon is based on random-to-axial statistical reorientation of the azochromophores following repetitive trans-cis-trans photoisomerization cycles. The resulting birefringence is inferred from analysis of the spectral shifts of the cavity Fabry–Perot longitudinal modes as a result of illumination. A large value of the birefringence of the order of 10−2 is noted after currently unoptimized durations of the order of 30′ in the 1.3–1.5 μm range with possible applications in optical storage at WDM telecom-compatible wavelengths.

Reflection second harmonic generation scanning microscope

Abstract We present a simple microscopy set-up towards the spatial mapping of second harmonic generation of non-linear structures. The sample surface is scanned through a microscope objective by an off-axis incident nanosecond Nd:YAG fundamental laser beam. The incident fundamental and reflected harmonic beams are collected by the same objective, which allows a close scan of the surface by using high amplification objectives. The scan of different organic material-based structures will be presented, showing a second harmonic intensity cartography of active materials like oriented DR1-PMMA electrooptic polymer and MNA crystals, with micron-scale resolution. This simple set-up provides a useful and compact tool to characterize non-linear active domains, in order to gain insight on materials as well as on functional properties of different polymer-based structures. Moreover, with appropriate selection of incident and reflected polarization states, different components of the d ijk tensor can be singled-out and lead to microscopic information on molecular organization and local variations.

Progress in erasable and permanent polymer based DFB-structures with multicolour tunable laser emission

Highly luminescent organic solid state media including molecular dye doped guest-host systems and novel conjugated polymers currently attract a lot of interest for application in photonic technology. We demonstrate organic solid-state lasers with broadly and continuously tuneable mode emission (Δλ = 40nm, FWHM < 1nm). Feed-back onto polymeric DFB-structures results from dynamic and permanent photoinduced in-plane gratings. A write and read - technique for easy and low cost fabrication of single and multiple grating devices is presented. The combination and optimization of tuneable gratings with specific confinement features as from different waveguiding formats open-up new approaches in integrated optics.