Daniele Rezzonico

Photochemical stability of nonlinear optical chromophores in polymeric and crystalline materials

We compare the photochemical stability of the nonlinear optical chromophore configurationally locked polyene 2-{3-[2-(4-dimethylaminophenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene} malononitrile (DAT2) embedded in a polymeric matrix and in a single-crystalline configuration. The results show that, under resonant light excitations, the polymeric compound degrades through an indirect process, while the DAT2 crystal follows a slow direct process. We show that chromophores in a crystalline environment exhibit three orders of magnitude better photostability as compared to guest-host polymer composites.

Electro-optic Charon polymeric microring modulators

We propose and demonstrate a new type of electro-optic polymeric microring resonators, where the shape of the transmission spectrum is controlled by losses and phase shifts induced at the asymmetric directional coupler between the cavity and the bus waveguide. The theoretical analysis of such Charon microresonators shows, depending on the coupler design, three different transmission characteristics: normal Lorentzian dips, asymmetric Fano resonances, and Lorentzian peaks. The combination of the active azo-stilbene based polyimide SANDM2 surrounded by the hybrid polymer Ormocomp allowed the first experimental demonstration of electro-optic modulation in Charon microresonators. The low-loss modulators (down to 0.6 dB per round trip), with a radius of 50 microm, were produced by micro-embossing and exhibit either highly asymmetric and steep Fano resonances with large 43-GHz modulation bandwidth or strong resonances with 11-dB extinction ratio. We show that Charon microresonators can lead to 1-V half wave voltage all-polymer micrometer-scale devices with larger tolerances to coupler fabrication limitations and wider modulation bandwidths than classical ring resonators.

Micromachining of ridge optical waveguides on top of He+-implanted β-BaB2O4 crystals by femtosecond laser ablation

We report on a technique for the fabrication of ridge optical waveguides on top of β-BaB2O4 (BBO) crystals. The BBO crystals were first implanted by He+ ions to form planar optical waveguides. In the second step, the femtosecond laser ablation technique was employed for micromachining of ridge-type optical waveguides. A thorough study of material-specific ablation parameters for BBO has been performed in order to achieve ablated structures with smooth sidewalls. A further process of Ar+ ion smoothing in a plasma chamber was used to reduce the sidewall roughness of the ablated ridges from 75 to 35 nm root mean square. We demonstrated optical waveguiding in these femtosecond-ablated plasma-treated waveguides and measured total propagation losses of less than 10 dB∕cm at 532 nm, making them suitable for nonlinear- and electro-optical applications.

High-finesse laterally coupled organic-inorganic hybrid polymer microring resonators for VLSI photonics

We produced laterally coupled optical microring resonators having high finesse (F/spl sime/17 at 1.5-/spl mu/m wavelength) using a two-step patterning technique based on optical photolithography. The technique used allows us to separately control the height of both ring and port waveguides and structure submicrometer gaps. The resonance spectrum of microrings with radii of 50 /spl mu/m made of an organic-inorganic hybrid polymer have an extinction ratio of about 12 dB and a filter bandwidth /spl delta//spl lambda//spl sime/0.28 nm (full-width at half-maximum) at a wavelength /spl lambda/=1547.78 nm. We show that the resonances can be thermooptically tuned by 0.2 nm//spl deg/C, thus allowing us to modulate the transmission of the through port signal.

Photostability studies of π-conjugated chromophores with resonant and nonresonant light excitation for long-life polymeric telecommunication devices

Theoretical and experimental studies of molecular photodegradation in π-conjugated chromophores with resonant and nonresonant excitation relative to the lowest-energy electronic transition of the chromophore are performed. The limitations of previous photodegradation models are discussed, and new models that overcome these limitations and provide more accurate estimates of chromophore photostability are presented. In particular, the necessity of considering multiple degradation pathways in the analysis of photobleaching studies is shown. Photostability studies of a dihydrofuran thiophene-bridged dicyanomethylene based chromophore (FTC) employing 1.55-μm excitation reveal that the photoinitiated decay kinetics are biphasic. We present what we believe to be a new, double-pathway photodegradation model capable of describing this behavior. Through investigations employing the singlet-oxygen quencher bis(dithiobenzil)nickel, photooxidation is shown to be one of the photodegradation pathways, and the ability of a quencher to inhibit chromophore photooxidation is quantified. The studies presented here provide insight into the mechanism of photochemical degradation of π-conjugated chromophores for devices operating in the visible and at telecommunication wavelengths.

Electro-optic polymer microring resonators based on Charon coupler design

We propose and demonstrate a new type of electro-optic microresonators, where the shape of the transmission spectrum is controlled by losses and phase shifts induced at the asymmetric coupler between the cavity and the bus waveguide.

Electro-optical microring resonators in epitaxial crystalline organic and ion sliced inorganic materials

Electro-optically tunable microring resonators and waveguides were fabricated in submicrometer thin ion-sliced LiNbO3 films and epitaxially grown organic single crystalline materials. The organic crystalline waveguides show large electro-optical effects and superior photo and thermal stability as compared to polymeric materials. Electro-optical resonatorsmicroring resonators crystalline epitaxial organic material son sliced.

Two-step photolithographic technique for laterally coupled hybrid polymer microring resonators

We propose a simple and fast two-step patterning technique that allows controlling the gap between rings and port waveguides in lateral couplers, as well as independently adjusting the height of the different waveguides. Despite the proximity mode exposure, inducing a strong diffraction of the UV light at the apertures on the mask, the patterning technique resulted very precise, with 0.30 mum wide gaps between the ports and the ring.