Low power consumption integrated acousto-optic filter in domain inverted LiNbO3 superlattice.

We report on an integrated acousto-optic filter in domain inverted LiNbO3 using a coplanar electrode configuration, which can achieve complete optical switching at electrical powers as low as 50 mW. These values are more than one order of magnitude lower than previously reported results [Opt. Lett. 34, 3205 (2009)]. In order to design the low power consumption devices, we have calculated surface acoustic wave excitation, propagation and acousto-optic interaction in the domain inverted LiNbO3 superlattice using scalar approximation and FEM analysis. Results from both modeling techniques are in good agreement with the experiments, including direct measurement of the acoustic displacement using laser interferometry and acousto-optic performance.

Integrated acousto-optic polarization converter in a ZX-cut LiNbO(3) waveguide superlattice.

We report an integrated acousto-optic polarization converter exploiting a novel surface acoustic superlattice (S-ASL) transducer. The S-ASL transducer is made of a ZX-cut periodically poled lithium niobate (PPLN) crystal with uniform coplanar electrodes for surface acoustic wave (SAW) generation. For a PPLN period of 20 microm the SAW is excited at an rf of about 190 MHz, while the phase matching occurs at an optical wavelength of around 1456 nm. The measured mode conversion efficiency of 90% at an input rf power of 1 W and the 3 dB optical bandwidth of 2.5 nm confirm the confinement of the SAW between the electrode gap and the constructive interaction along the whole 10 mm electrode length.

Fiber strain sensor based on a pi-phase-shifted Bragg grating and the Pound-Drever-Hall technique.

A fiber strain sensor based on a p-phase-shifted Bragg grating and an extended cavity diode laser is proposed. Locking the laser frequency to grating resonance by the Pound-Drever-Hall technique results in a strain power spectral density S(epsilon) (f) = (3 x 10(-19) f(-1) +2.6 x 10(-23)) epsilon(2)/Hz in the Fourier frequency range from 1 kHz to 10 MHz (epsilon being the applied strain), corresponding to a minimum sensitivity of 5 pepsilon Hz(-1/2) for frequencies larger than 100 kHz.

Very low voltage single drive domain inverted LiNbO(3) integrated electro-optic modulator.

Domain inversion is used in a simple fashion to improve significantly the performance of a waveguide electro-optic modulator in z-cut LiNbO(3). The waveguide arms of the Mach-Zehnder interferometer are placed in opposite domain-oriented regions under the same, narrower and more efficient electrode, so that opposite phase shifts (push-pull effect) can still be achieved despite the arms being subjected to the same electric field. Switching voltages close to 2 V are obtained, which allow 10Gb/s modulation with inexpensive drivers, such as those used for electro-absorption modulators, which deliver driving voltages well below 3V.

Slow light in periodic superstructure Bragg gratings.

A theoretical and experimental analysis of group velocity reduction in periodic superstructure Bragg gratings is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the wavelength of optical communications is reported using a Moiré fiber grating.

Beam dynamics and wave packet splitting in a periodically curved optical waveguide: multimode effects.

A theoretical and experimental analysis of beam dynamics and wave packet splitting of light in a periodically bent optical waveguide, a phenomenon recently observed [Phys. Rev. Lett. 94, 073002 (2005)] which is the optical equivalent of adiabatic stabilization of atoms in intense and high-frequency laser fields, is presented in the multimode operational regime. Inhibition of wave packet splitting is theoretically predicted and experimentally observed for higher-order mode excitation.

Observation of wave packet dichotomy and adiabatic stabilization in an optical waveguide.

We report on the first experimental observation of wave packet dichotomy and adiabatic stabilization of light in a periodically bent optical waveguide in analogy with similar behavior of atoms in high-frequency strong laser fields.

Ray and wave instabilities in twisted graded-index optical fibers.

We study ray and wave propagation in an elliptical graded-index optical fiber or lens with a twisted axis and show analytically the existence of an instability for both ray trajectories and beam moments in a finite range of axis twist rate embedded within the spatial frequencies of periodically focused rays for the untwisted fiber. By considering the paraxial ray equations and the paraxial wave dynamics in a rotating frame that follows the fiber axis twist, we reduce the dynamical problem of ray trajectories to the classical Blackburn's pendulum, which shows a dynamical instability, corresponding to classical diverging trajectories, due to the competing effects of confining potential, Coriolis force, and centrifugal force. A closed set of linear evolution equations for generalized beam moments are also derived from the paraxial wave equation in the rotating reference frame, revealing the existence of a dynamical moment instability in addition to the trajectory instability. A detailed analysis of beam propagation is presented in case of a Gaussian beam, and different dynamical regimes are discussed.

Quantum-mechanical analogy of beam propagation in waveguides with a bent axis: dynamic-mode stabilization and radiation-loss suppression.

Wave propagation in an optical waveguide with a bent axis is studied under the scalar and paraxial wave approximations, and the quantum mechanical analogy with the electron dynamics in an atomic potential interacting with an intense electromagnetic field is highlighted. In particular we show that for a truncated parabolic waveguide with a periodically curved axis, a dynamic mode splitting with reduced radiation losses can be observed, which is fully analogous to the phenomenon of wave packet dichotomy and ionization quenching found in strong-field atomic physics.

Brucellosis: unusual presentations in two adolescent boys.

Two boys presented with variable signs and symptoms of infectious disease that challenged diagnosis. One of the two patients had aortic valve vegetations and lower extremity aneurysms, and the other had calvarial osteomyelitis, epidural abscess, pleural effusions, and pulmonary nodules. Only after a battery of bacterial and fungal agglutination tests was the unsuspected diagnosis made in each of brucellosis from Brucella canis.

Efficacy and safety of ampicillin/sulbactam and cefuroxime in the treatment of serious skin and skin structure infections in pediatric patients. UNASYN Pediatric Study Group.

BACKGROUND: Pediatric skin and skin structure infections are often polymicrobial and require empiric therapy effective against pathogens that may be resistant to many antimicrobial agents. The present study tested the efficacy and safety of a parenteral beta-lactam/beta-lactamase inhibitor combination, ampicillin/sulbactam, and a beta-lactamase-stable cephalosporin, cefuroxime, in serious pediatric skin and skin structure infections requiring hospitalization and parenteral antimicrobial therapy. METHODS: This was a multicenter, randomized, prospective, comparative open label trial that enrolled patients 3 months through 11 years of age. Patients received 150 to 300 mg/kg/day ampicillin/sulbactam in equally divided intravenous doses every 6 h. Cefuroxime was given in a dosage of 50 to 100 mg/kg/day either intravenously or intramuscularly in equally divided doses every 6 or 8 h. Maximum treatment was not to exceed 14 days. Patients could receive subsequent oral antimicrobial treatment at the investigator's discretion. RESULTS: At final evaluation for clinical efficacy, 78.0% (n = 46) of the 59 evaluable patients who received ampicillin/sulbactam were cured and 22.0% (n = 13) were improved. The respective values for the 39 evaluable patients treated with cefuroxime were 76.9% (n = 30) and 23.1% (n = 9). At the end of treatment all pathogens were eradicated from 93.2% (n = 55) of 59 patients treated with ampicillin/sulbactam and from 100% of 39 who received cefuroxime. There were no significant differences between treatments in clinical or bacteriologic efficacy. Both ampicillin/sulbactam and cefuroxime were well-tolerated. CONCLUSION: Both ampicillin/sulbactam and cefuroxime provide safe and effective parenteral antibiotic therapy in pediatric patients with serious skin and skin structure infections.

Pneumocystis carinii pneumonia in infants after heart transplantation.

Although the reported incidence of Pneumocystis carinii pneumonia after heart transplantation in adults ranges from 3% to 40%, data are lacking regarding the incidence in the pediatric heart transplantation population. A retrospective review was performed on 152 infants (0 to 12 months of age) undergoing transplantation from November 1985 through December 1993 who survived at least 6 months after heart transplantation. Patients did not receive postoperative Pneumocystis carinii prophylaxis. Ten episodes (7%) were diagnosed in four neonates and six infants. The mean postoperative time to Pneumocystis carinii diagnosis was 5 months (range 3 to 9 months). Features of Pneumocystis carinii included hypoxia and tachypnea (10 of 10), progressive interstitial infiltrates (8 of 10), and persistent right middle lobe consolidation (1 of 10). Pneumocystis carinii was diagnosed with the use of bronchoscopy in eight cases and by open lung biopsy in two cases. Mean CD4 count available on five patients at the time of Pneumocystis carinii diagnosis was 413/mm3 (range 158 to 1358); 5 of 37 patients receiving antithymocyte induction had Pneumocystis carinii versus 5 of 115 patients who did not receive induction (p = 0.05). Patients were at increased risk for the development of Pneumocystis carinii if they had more than two episodes of rejection during the first year after heart transplantation (p = 0.04). All cases were successfully treated with trimethoprim/sulfamethoxazole. The incidence of Pneumocystis carinii in infant heart transplantation recipients is approximately 7% and appears most frequently in the first 6 months after the operation. Increased risk for Pneumocystis carinii may be related to early antithymocyte induction and increased episodes of rejection.