Interplay between multiple scattering and optical nonlinearity in liquid crystals

We discuss the role played by time-dependent scattering on light propagation in liquid crystals. In the linear regime, the effects of the molecular disorder accumulate in propagation, yielding a monotonic decrease in the beam spatial coherence. In the nonlinear case, despite the disorder-imposed Brownian-like motion to the self-guided waves, self-focusing increases the spatial coherence of the beam by inducing spatial localization. Eventually, a strong enhancement in the beam oscillations occurs when power is strong enough to induce self-steering, i.e. in the non-perturbative regime.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Self-trapping of light using the Pancharatnam-Berry phase

Since its introduction by Berry in 1984, the geometric phase has become of fundamental importance in physics, with applications ranging from solid-state physics to optics. In optics, the Pancharatnam-Berry phase allows the tailoring of optical beams by a local control of their polarization. Here, we discuss light propagation in the presence of an intensity-dependent local modulation of the Pancharatnam-Berry phase. The corresponding self-modulation of the wave front counteracts the natural spreading due to diffraction; i.e., self-focusing takes place. No refractive index variation is associated with the self-focusing: The confinement is uniquely due to a nonlinear spin-orbit interaction. The phenomenon is investigated, both theoretically and experimentally, by considering the reorientational nonlinearity in liquid crystals, where light is able to rotate the local optical axis through an intensity-dependent optical torque. Our discoveries pave the way to the investigation of a new family of nonlinear waves featuring a strong interaction between the spin and the orbital degrees of freedom

Direct digital control of an efficient silicon+lequid crystal phase shifter

We demonstrate a phase shifter based on a silicon slot waveguide infiltrated with liquid crystal. We achieve a phase shift of 73 pi for a 5V drive voltage, with a voltage-length product of 0.022V.mm around 1V. We can drive the phase shifter directly with a 1V, duobinary pulse-width-modulated signal, allowing direct digital CMOS control of an analog optical phase shifter

Light modulation in Silicon photonics by PZT actuated acoustic waves

Tailoring the interaction between light and sound has opened new possibilities in photonic integrated circuits (PICs) that ranges from achieving quantum control of light to high-speed information processing. However, the actuation of sound waves in Si PICs usually requires integration of a piezoelectric thin film. Lead Zirconate Titanate (PZT) is a promising material due to its strong piezoelectric and electromechanical coupling coefficient. Unfortunately, the traditional methods to grow PZT on Silicon are detrimental for photonic applications due to the presence of an optical lossy intermediate layer. In this work, we report integration of a high quality PZT thin film on a Silicon-on-insulator (SOI) photonic chip using an optically transparent buffer layer. We demonstrate acousto-optic modulation in Silicon waveguides with the PZT actuated acoustic waves. We fabricate inter digital transducers (IDTs) on the PZT film with a contact photo-lithography and electron-beam lithography to generate the acoustic waves in MHz and GHz range respectively. We obtain a V$_{\pi}$L $\sim$ 3.35 V$\cdot$cm at 576 MHz from a 350 nm thick gold (Au) IDT with 20 finger-pairs. After taking the effect of mass-loading and grating reflection into account, we measured a V$_{\pi}$L $\sim$ 3.60 V$\cdot$cm at 2 GHz from a 100 nm thick Aluminum (Al) IDT consisting of only 4 finger-pairs. Thus, without patterning the PZT film nor suspending the device, we obtained figures-of-merit comparable to state-of-the-art modulators based on SOI, making it a promising candidate for broadband and efficient acousto-optic modulator for future integration

Transient intraluminal diverticulum of the esophagus: A significant flow artifact

Esophagography in 12 patients showed a characteristic oval-to oblong-shaped barium collection surrounded by a thin radiolucent margin. The collection closely resembled an intraluminal diverticulum. Twelve patients demonstrated these findings, 6 on single-contrast and 6 on double-contrast examinations. These findings were not reproducible on repeat barium swallows, and endoscopy failed to demonstrate an intraluminal diverticulum. Nine of the patients underwent esophagectomy and esophageal substitution. Pathologic examination of the gross specimen did not reveal evidence of intraluminal diverticula. The association of this radiologic appearance in patients with moderately severe motility disorder of the esophagus is emphasized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48158/1/261_2005_Article_BF01887813.pd