Andrea Guarino

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.

Refractive indices of Sn2P2S6 at visible and infrared wavelengths

We report on the refractive indices of Sn2P2S6 crystals in the wavelength range 550 - 2300 nm. The measurements are performed at room temperature using the minimum deviation method. The dispersion is described by a two oscillator model yielding the oscillator energies and strengths (Sellmeier parameters) for all polarization directions. The rotation of the indicatrix in the mirror plane and the direction of the optical axes have also been determined in the wavelength range lambda= 550-2200 nm.

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.

Second harmonic generation of continuous wave ultraviolet light and production of β-BaB2O4 optical waveguides

We report on the generation of continuous-wave (cw) ultraviolet (UV) laser light at λ=278nm by optical frequency doubling of visible light in β-BaB2O4 waveguides. Ridge-type waveguides were produced by He+ implantation, photolithography masking, and plasma etching. The final waveguides have core dimension of a few μm2 and show transmission losses of 5dB∕cm at 532nm and less than 10dB∕cm at 266nm. In our first experiments, a second harmonic power of 24μW has been generated at 278nm in an 8mm long waveguide pumped by 153mW at 556nm.

Optical waveguides in Sn(2)P(2)S(6) by low fluence MeV He+ ion implantation.

Optical waveguides in nonlinear crystals of Sn₂P₂S₆ have been produced by He⁺ ion implantation. Best results are obtained with a fluence about Phi = 0.5 middot 10¹⁵ ions/cm² and for hybrid _n1-mode. The depth of the induced optical barrier is Delta_n1 = -0.07 at lambda = 0.633mum.

Epitaxial K 1−x Na x Ta 0.66 Nb 0.34 O 3 thin films for optical waveguiding applications

Monomodal slab waveguides in lattice-matched epitaxial thin films of paraelectric potassium sodium tantalate niobate (x≈0.02) on paraelectric potassium tantalate substrates without surface polishing have been fabricated for the first time, to the best of our knowledge. A surface roughness of 21 nm (rms) has been measured by atomic force microscopy. The film thickness, d=1.4 μm, and refractive index contrast, Δn=8×10−3, have been deduced from the intensity profile of the guided mode at λ=633 nm.

Nondestructive method for the characterization of ion-implanted waveguides

A new method, called barrier coupling, for coupling light into ion-implanted waveguides is presented in analogy to prism coupling. Light is coupled by frustrated total reflection at the barrier region of decreased refractive index by proper variation of the incident angle. Effective indices of guided modes are determined by the minima of the non-incoupled reflected light. The method is used for the determination of the effective indices of an ion-implanted waveguide in KNbO3. It is simpler than most other techniques, more accurate, and nondestructive.

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.