Showing papers by "James Taylor published in 1996"

Direct continuous-wave measurement of n(2) in various types of telecommunication fiber at 1.55 microm.

Abstract: A method for measuring the nonlinear refractive index of optical fibers with an error of less than 5% is demonstrated. The technique is based on measuring the nonlinear phase shift experienced by a dual-frequency beat signal, permitting a simple, highly sensitive, accurate, repeatable, and easily automated measurement procedure and sampling. Measurements of the nonlinear coefficient in standard telecommunication, dispersion-shifted, and a number of dispersion-compensated fibers are presented.

Giant Radio Pulses from a Millisecond Pulsar

Abstract: We have observed 1.7 × 106 individual pulses from the millisecond pulsar PSR B1937+21. About one pulse in 10,000 has more than 20 times the mean "pulse-on" flux density, and individual pulses as large as 300 times the average were observed. Comparable behavior has previously been observed only for the Crab pulsar. Giant pulses from PSR B1937+21 are seen in both the main pulse and interpulse components, and their amplitude distribution has roughly a power-law shape. Strong pulses differ greatly from the average emission: they are narrower, systematically delayed by some 40-50 μs, and many are nearly 100% circularly polarized. In addition to their potential importance for elucidating the physics of the emission region, the giant pulses may be useful for high precision timing measurements.

Visible continuous-wave laser transitions in Pr(3+):YLF and femtosecond pulse generation.

Abstract: Fourteen new cw, visible laser transitions have been observed in Pr3+:YLF, several of which have exhibited modest tunability. The 3P0 − 3H6 transition near 613 nm has been shown to have a tunable linewidth of ~1 nm, which, for the first time to our knowledge, has permitted the direct production of femtosecond pulses in the visible from a cw solid-state laser by Kerr-lens mode locking.

Measurement of normalization factor of n(2) for random polarization in optical fibers.

Abstract: The 8/9 normalization coefficient for the nonlinear refractive index in nonpolarization-maintaining optical fibers is confirmed directly by measurement of the ratio of the self- and cross-phase modulation coefficients for two orthogonal polarizations. The nonlinear phase shift is accurately measured with a dual-frequency beat signal as a pump source.

The association between parental health beliefs and immunization status among children followed by private pediatricians.

Abstract: To determine the association between parental health beliefs and the immunization status of their children, parents of children seen in two private pediatric practices completed a questionnaire on attitudes about immunizations. Five components of health beliefs were surveyed: perceived benefits of immunizations, susceptibility to diseases prevented by immunizations, severity of those diseases, parental feelings of self-efficacy in promoting their child's health, and barriers to immunization. Responses to the health-beliefs statements were transformed to an ordinal scale between 1 and 6, with ‘6’ corresponding to strongly positive feelings about immunizations. Immunization data were abstracted from practice medical records. Overall, 162/194 (83.3%) study children were fully immunized. There were no significant differences between parents of fully immunized children and those of under-immunized children in total health-beliefs score or for the benefits, susceptibility, severity, or barriers components. Self...

Self-starting Kerr-lens mode-locked femtosecond Cr(4+):YAG and picosecond Pr(3+):YLF solid-state lasers.

Abstract: We have observed true self-starting Kerr-lens mode locking in two distinct solid-state laser systems operating at room temperature by optimizing the cavity geometry to maximize the amplitude modulation with respect to the intracavity power variation. Pulses of 15 ps have been obtained from a Pr3+:YLF laser system operating at 607 nm, and 53-fs pulses have been obtained from Cr4+:YAG at 1.54 μm.

Gain switched DFB laser diode pulse source using continuous wave light injection for jitter suppression and an electroabsorption modulator for pedestal suppression

Abstract: 4 ps pulses with low temporal jitter (0.6 ps) and reduced pedestal (> 25 dB extinction) have been generated from a 1548 nm gain switched distributed feedback laser diode (DFB) pulse source at 2.5 GHz using continuous wave (CW) light injection for jitter suppression and an electroabsorption modulator (EAM) for pedestal suppression.

Methodological issues in determining rates of childhood immunization in office practice. A study from pediatric research in office settings (PROS).

Abstract: Objective: To compare 3 methods for measuring pediatric office immunization rates. Design: Retrospective and prospective cross-sectional surveys. Patients: Children 2 and 3 years old from 15 pediatric practices in 11 states. Methods: Immunization rates were determined for each practice using 3 methods. The Consecutive method used data from the practice's medical records of patients seen consecutively in the office; the Chart method used data from randomly selected practice medical records; and the Active method (reference standard) used a combination of medical record data with a telephone interview to collect additional immunization data and current patient status, using data only on current patients. Analyses were based on a mean of 57, 62, and 51 (Consecutive, Chart, and Active method, respectively) patients per practice. Patients were considered fully immunized if they had received 4 doses of DTP/DT vaccine, 3 doses of OPV/IPV, and 1 dose of MMR vaccine by their second birthday. Comparisons were made using the paired t test. Results: The mean immunization rate by method was Consecutive, 81.5% (range, 51%-97%); Chart, 71.6% (range, 42%-94%); and Active, 79.6% (range, 53%-96%). Within a given practice, the differences between methods varied considerably (0 to 28 percentage points). The mean difference from the reference standard Active method was 8 percentage points ( P P =.36) for the Consecutive method. The largest difference was between the Consecutive and Chart methods (mean difference, 9.9 percentage points; P =.003). Practitioners uniformly found the Consecutive method easiest to implement. Conclusions: Practice-specific immunization rates are one of the few objective measures of the quality of preventive pediatric care. Pediatric practices monitoring their immunization rates should consider using the Consecutive method, a simple, acceptable, and valid measure of practice immunization rate. Arch Pediatr Adolesc Med. 1996;150:1027-1031

Single-frequency erbium fibre laser using the twisted-mode technique

Abstract: A single-frequency erbium fibre laser operating at 1.534 /spl mu/m is demonstrated. Single frequency operation is achieved using the twisted mode technique. Using a self-heterodyne technique a detector-limited linewidth of 10 kHz was measured.

Measurement of n/sub 2/ of various types of fibres used for ultra-high bit rate transmission

Abstract: A reliable and simple method for measuring n/sub 2//A/sub e/ff is described This technique has the advantage of making use of CW lasers only and, therefore, the power measurements become considerably more accurate than when pulses are employed. Also, the fact that equal intensity spectral lines are used represents a great simplification of the calculations involved in determining the maximum nonlinear phase shift. The value of n/sub 2//A/sub e/ff was measured for several fibres with different compositions, namely, single mode fibres (SMF), five dispersion shifted fibres (DSF) and eight dispersion compensating fibres (DCF), four with Ge-doping only and four with Ge and F-doping. The error in the values obtained was never greater than 10% and agreed well with the fibre's dopants concentrations and profile.

10 GHz 3 ps actively mode-locked ring laser incorporating a semiconductor laser amplifier and an electroabsorption modulator

Abstract: The authors report a novel actively mode-locked unidirectional semiconductor ring laser constructed from discrete fibre pigtailed components. When driven at 10 GHz, the laser produces near transform-limited pulses of 3 ps duration.

Risk factors for the infant prone sleep position.

Abstract: Objective: To identify parental characteristics associated with infants being placed to sleep in the prone position. Study Design: Cross-sectional survey. Patients: Randomly selected King County, Washington, infants born on the same days as King County infants who died of sudden infant death syndrome between November 1992 and October 1994. Methods: Parents of study infants responded to a telephone interview about sleep position in their infants. Parents were asked how they usually put their infants to bed during the previous 2 weeks, and if they were aware of any recent advice on sleep position in young infants. Demographic data were also collected during the telephone interview. Logistic regression was used to identify infant and parental characteristics associated with the prone sleep position. Results: Parents of 178 infants were interviewed; 28.1% responded that their infants usually slept prone, 66.9% slept nonprone, and 5% had no usual sleep position. Parents who were unaware of sleep position advice were more likely to place their infants prone than those who were aware of this advice (odds ratio, 3.5; 95% confidence interval, 1.5-7.8). Among parents who were aware of sleep position advice, mothers younger than 20 years were more than 10 times as likely to place their infants prone than were older mothers (odds ratio, 10.7; 95% confidence interval, 1.1-107.0). For those who were unaware of sleep position advice, single mothers were more likely to place their infants prone (odds ratio, 14.0; 95% confidence interval, 1.5-133.2). Single mothers and parents of low-birth-weight infants were more likely to be unaware of recent medical advice regarding optimal sleep position for infants. Conclusions: The results of this study may provide direction to future efforts to encourage nonprone sleeping. Knowledge of the risk is associated with decreased use of prone sleep position. Single mothers should be targeted for intensive educational efforts regarding the hazards of prone sleeping. Among teenage mothers, awareness of the association between prone sleeping and sudden infant death syndrome may not be adequate to change behavior; educational interventions that are more focused for this age group may be needed. Arch Pediatr Adolesc Med. 1996;150:834-837

On-line optimal reactive power flow by energy loss minimization

Abstract: A method for online application of optimal reactive power dispatch based on total energy loss minimization (ELM) is presented. In this approach the total energy loss from the present instant over the next hour is minimized. The method uses the load forecast during this period. All the continuous and discrete control variables are adjusted on an hourly basis. During the hour, any voltage constraint violations are removed by adjusting the VArs/voltages of generators every 15 minutes. A detailed study of a sample network is given. The ELM and power loss minimization (PLM) methods are compared by using the sample network. As seen in simulation results, the voltage profile from the ELM method is more satisfactory than that from the PLM method. In addition, the total energy loss during the specified hour which is found from the ELM method is lower than that from the PLM method. Finally, the proposed method is more likely to find feasible solutions, while the PLM method can have difficulty doing so.

All-solid-state Kerr lens mode-locked Cr4+:forsterite laser

Abstract: We describe a compact, self-mode-locked. Tunable (in the second telecommunications window) all-solid-state. Cr/sup ++/:forsterite laser generating transform limited sub 70 fs pulses.

A resonant cascade-raman radiation source

Abstract: A resonant cascade-Raman radiation source comprises a long optical fibre which is adapted for producing Raman radiation when pump radiation is passed along it. One or more additional optical fibres are coupled across the main optical fibre to produce individual optical resonator circuits each of which resonates at a particular Stokes frequency. Cascaded Raman scattering occurs within the device, allowing access to higher Stokes components via suitably-positioned optical coupler within one of the loops. In one embodiment, the device acts as an optical amplifier, and in another it acts as an efficient radiation source (laser). Applications include optical telecommunications and remote sensing, including pollution monitoring.

Ultrahigh-Bit-Rate Optical Sources and Applications

Abstract: Various techniques are described for the generation of high repetition rate high-quality soliton pulse trains in the range 10 GHz-1 THz. Emphasis is placed on the technique of nonlinear conversion of an optical beat signal in dispersion-modified fibre. This can be achieved by a number of methods, including tapered or dispersion-decreasing fibre, step-like dispersion-profiled fibre and comb-like dispersion-profiled fibre. In addition, self-Raman scattering has been demonstrated as a powerful technique for ultrashort pulse generation and excellent mark space ratio operation. Techniques based on phase-modulated sideband extraction and direct modulation using electroabsorption modulators operating in the 10-60 GHz regime are also described.

Resist application effects on chemically amplified resist response

Abstract: Chemically amplified negative resist films of Shipley SAL 605 at 1.0 μm thickness show a statistically optimized sensitivity that is twice that observed with 0.5 μm films when exposed to x rays from an electron storage ring. Because of the large ‘‘depth of focus’’ of proximity x‐ray lithography, the differences between thick and thin films are due to resist chemical and physical effects and processing conditions, not to the exposure process. Using identical processing conditions, 1.0‐μm‐thick films showed 34% larger linewidths than 0.5 μm films for isolated lines from one mask with a target linewidth of 0.215 μm. Gel permeation chromatography results indicated that there was no dependence of resin or crosslinker concentration on thickness of the applied film. The photogenerated acid and residual solvent were quantified prior to postexposure bake, and neither was able to explain the apparent sensitivity dependence on thickness. The work suggests that some of the differences arises in the resist application process because of the ability of the thicker film to retain small molecular weight species which facilitate the linewidth production. This implies that thinner films should show better resolution purely because of chemical and physical factors in the resist film.

Demonstration of the feasibility of dual frequency operation of an electroabsorption modulator for demultiplexing in a 16 channel 40 Gbit/s OTDM system

Abstract: It is shown that, by driving an electroabsorption modulator with a dual-frequency RF drive, it is possible to decrease the duty cycle attainable to as little as 3.5%, making it possible to demultiplex from 40 to 2.5 Gbit/s using a single device.

New Visible CW. Laser Transitions in Pr3+:YLF and Femtosecond Pulse Generation

Abstract: Fourteen new cw, visible laser transitions have been observed in Pr3+:YLF, several of which have exhibited modest tunability. The 3P0 - 3H6 transition around 613 nm has been shown to have a tunable linewidth of ~1nm, which, for the first time, has allowed the direct production of femtosecond pulses in the visible from a cw solid state laser using Kerr lens mode-locking.

Fuzzy-logic controller synthesis for electro-mechanical systems with nonlinear friction

Abstract: We report on preliminary results in developing a new method for the synthesis of fussy-logic controllers for amplitude-sensitive nonlinear plants based on sinusoidal-input describing-function methods. This technique exploits the fact that two traditional classes of fuzzy-logic controllers are, in functional terms, of the proportional-plus-derivative (PD) and proportional-plus-integral (PI) types. It involves the direct generation of the membership functions and output levels based on the "frequency response" of the nonlinear plant in the describing-function sense. The resulting fuzzy-logic controller obtained in this paper includes derivative action in an inner-loop feedback path (nonlinear rate feedback) and nonlinear PI compensation in the forward path; the performance of the closed-loop system is, by design, quite insensitive to reference-input amplitude. An illustration of the method and its effectiveness is provided, based on a prototypical position control problem where a servomotor plus mechanical load are characterized by torque saturation and nonlinear friction.

An intelligent front end for control system implementation

Abstract: We present a new expert-system "front end" or design advisor for implementing systems (DAIS) for use in conjunction with a commercial digital control system environment, e.g., the Elsag Bailey INFI 90 System. The objective of DAIS is to make it substantially easier for applications engineers to make effective use of the broad spectrum of capabilities of this and similar hardware and software systems for industrial controls implementation. This concept is of quite general applicability for industrial controls implementation environments.

All-Solid-State Diode-Pumped Tunable Femtosecond Cr:LiSAF Oscillator/Regenerative Amplifier

Abstract: An all-solid-state, diode-pumped, tunable femtosecond Cr:LiSAF KLM oscillator and 25 kHz microjoule regenerative amplifier is reported. The oscillator delivers pulses as short as 24 fs.

Q-switching of Er/sup 3+//Yb/sup 3+/-doped fiber laser using backscattering from a fiber ring interferometer

Abstract: Summary form only given. High-peak-power pulsed lasers operating around 1.5 /spl mu/m and generating nanosecond pulses at repetition rates from hundreds hertz to tens of kilohertz are of interest for various applications in eye-safe ranging, remote sensing and in fiber reflectometry etc. A number of techniques have been used. Here, we demonstrate a novel self-Q-switched Er-doped fiber laser generating 5-15 nsec pulses with a tunable repetition rate from 100 Hz to 10 kHz in all-optical-fiber configuration without using any active intracavity modulation.