Single-channel transmission in dispersion management links inconditions of very strong pulse broadening: application to 40 Gb/ssignals on step-index fibers

The dynamic behavior of single-channel transmission on standard fibers with strong dispersion management has been theoretically and numerically analyzed. A single pulse and a pseudorandom pulse sequence have been compared in order to highlight the relevant role played by pulse interaction. A semianalytical theory of the bandwidth evolution demonstrates that the introduction of prechirp is very important for controlling the single pulse propagation and numerical results show that such a chirp also permits to limit the nonlinear pulse interaction when other pulses are present. Simulations of a 40 Gb/s return-to-zero (RZ) system operating in links encompassing step-index fibers, by adopting a periodical compensation of the chromatic dispersion have been performed and results show that a record distance of 1300 km can be achieved with an amplifier spacing of 100 km. A compensation of the fiber third order dispersion would extend the transmission to 1800 km, which corresponds to the limits imposed by the amplified spontaneous emission (ASE) noise of the optical amplifiers     

Experimental broadband ultrasonic transducers using PVF2 piezoelectric film

Broadband ultrasonic transducers using PVF2 piezoelectric plastics films, combining efficient transduction with extremely wide and uniform passbands, have been fabricated using very simple procedures without any critical tolerances Frequency spectra of impulsed transducers using films of 25 and 50 ?m thickness, centred at 10 and 5 MHz, respectively, are shown.     

Cross-phase modulation in polarization shift-keying lightwave systems

We investigate the effect of cross-phase modulation in wavelength-division-multiplexed polarization-modulation lightwave systems. Analytical expression for the Q factor penalty in terms of signal power, the number of channels, and other parameters are derived. The theory is compared with numerical experiments.     

On the design of multipass dye laser amplifiers

We describe a universal method for designing multipass dye laser amplifiers typically pumped longitudinally by Q-switching high-energy pulses. The method is based on a set of normalized curves for the gain and on the experimental measurement of the amplifier noise. In this way, the method tries to maximize the gain and to reduce or control the losses in terms, of amplified spontaneous emission and reabsorption of the signal by the uninverted amplifying material. It has been tested to design and optimize a high-gain multipass amplifier for picosecond pulses. The realized system has a compact geometry and offers a gain of over 36 dB, with output pulse energy of 14 μJ and few megawatts of peak power     

Intra-incisional prophylactic antibiotics for dermatologic surgery

OBJECTIVE: To determine the efficacy of intra-incisional antibiotics in decreasing the risk of wound infections in cutaneous surgery. DESIGN: Prospective, blinded, randomized, placebo-controlled trial conducted during an 8-month period. SETTING: A private practice Mohs micrographic surgery referral center. PATIENTS: Seven hundred ninety consecutive patients referred for Mohs surgery or other dermatologic surgery were randomized to receive anesthesia either with study compound or placebo. The 2 groups were equivalent with respect to age and sex distribution and the lesions treated were similar in character. No patients were withdrawn for adverse effects. INTERVENTIONS: Patients received local anesthesia before surgery with either buffered lidocaine hydrochloride or a solution consisting of nafcillin sodium in buffered lidocaine. MAIN OUTCOME MEASURES: All surgical wounds were evaluated in a blinded fashion at the time of suture removal (5-7 days) and scored according to a standardized assessment chart based on erythema, edema, and the presence of purulent discharge. RESULTS: Seven hundred ninety consecutive patients with 908 surgical wounds were enrolled in this study. A total of 12 wound infections were recorded. Eleven (2.5%) of these occurred in the control group, while only 1 (0.2%) occurred in the nafcillin group. This difference was highly significant (P = .003). Observers were blinded to patient groupings particularly for surgical wound scoring. CONCLUSIONS: This study offers strong supporting data for the use of a single intra-incisional dose of an antibiotic administered immediately before dermatologic surgery. The use of nafcillin and buffered lidocaine solution is inexpensive, safe, convenient, and effective.     

Development and test of a 500-kW, 8-GHz gyrotron

An 8-GHz gyrotron that generates 500 kW and is capable of depressed collector operation is discussed. The output is extracted transversely from the circuit goes into two WR 137 rectangular waveguides through modified pillbox windows. The device will be used for lower hybrid heating of the FTU tokamak in Frascati, Italy, and has consequently been designed to produce over 400 kW when operated at a 4:1 VSWR. The current tube produces 1-s pulses every 10 min with the output power adjustable from approximately 150 to over 500 kW by changing only beam and mod anode voltage. The sensitivity to operating parameters is extremely low, making the tube easy to operate and unusually tolerant of variations in voltages and currents     

Transesophageal Phased Array for Imaging the Heart

A 3.5 MHz phased array has been developed for imaging the heart through the esophagus. The ultrasonic probe is fitted on the distal end of an Olympus gastroscope. Transesophageal images of the heart were obtained on ten patients. This paper describes the design and realization of the phased array and presents some clinical results obtained on patients.