Pulsed phase-locked loop calibration over frequency

This paper presents a method of correcting for unwanted phase shifts introduced by interchanging ultrasonic transducers and other measurement system components when using the pulsed phase-locked loop (PPLL) ultrasonic system. Theory is derived mathematically separating phase errors into their constituents. The relationship to a previously derived method of determining the number of periods into the tone-burst, at which the system samples, is established, and a method of adjusting this number to be an integer is presented. Implementation of the technology on a computer is demonstrated through experimental results on transducers of differing frequencies and diameters. Sensitivity to path-length is tested. This work has resulted in a straightforward means of calibrating transducers in conjunction with PPLL measurements using a single, fixed reference block     

High-spatial-resolution distributed strain measurement in optical fiber with rayleigh scatter

A method of measuring strain over 30-cm intervals to an accuracy of10 microstrain in unaltered low-loss communications-grade single-modeoptical fiber is presented. The method uses a tunable external cavity diode laser to measure the reflected intensity of a reflector-fiber system as a function of wavelength. This measurement is performed with no strain applied to the fiber to produce a reference and then again after a strain has been induced. Cross correlation of the Rayleigh scatter spectra from a selected section of fiber in the strained and unstrained states determines the spectral shift resulting from the applied strain.     

The power to play [games consoles]

Describes the technological and marketing factors that have transformed the games console into a powerful computing device and the home gateway to the Internet     

Volume current method for analysis of tilted fiber gratings

An analytic approach to calculate the radiation pattern (including the wavelength dependence, azimuthal distribution, and polarization dependence) of tilted fiber phase gratings using the volume current method (VCM) is introduced in this paper. Results for both uniform and apodized fiber gratings are derived and discussed, and a brief comparison to experimental measurements from practical devices is also made     

Distributed measurement of static strain in an optical fiber with multiple bragg gratings at nominally equal wavelengths

The Fourier transform relationship between the reflected light froma Bragg grating and the complex spatial modulation of the Bragg grating is used to produce a distributed strain sensing system. A tunable external cavity diode laser along with a reference reflector in anoptical fiber are used to produce a measurement of the phase and amplitude of the reflected light from the modulated Bragg grating as a function of wavelength. The system is demonstrated with 22 Bragg gratings in a single fiber on a cantilever beam and compared with foil strain gauge readings.     

Optical vector network analyzer for single-scan measurements of loss, group delay, and polarization mode dispersion

We present a method for measuring the complete linear response, including amplitude, phase, and polarization, of a fiber-optic component or assembly that requires only a single scan of a tunable laser source. The method employs polarization-diverse swept-wavelength interferometry to measure the matrix transfer function of a device under test. We outline the theory of operation to establish how the transfer function is obtained. We demonstrate the enhanced accuracy, precision, and dynamic range of the technique through measurements of several components.     

Product modification

For more than 20 years there has been a coherent programme of product modification in the UK, involving the introduction of low tar brands of cigarettes and the gradual reduction in average tar yields over the whole range of manufactured cigarettes. The sales-weighted average tar yield has declined from 20.8 mg/cigarette in 1972 to 11.0 mg/cigarette in 1993. To some extent potential benefits to established smokers have been offset by their tendency to 'compensate' for reduced nicotine yields. Investigating such aspects has formed one part of a wide-ranging research programme to monitor effects of modified products on health. Collectively the studies show benefits in terms of smoke intake and health outcome related to reduced tar cigarettes, but the success achieved in reducing average tar yields and narrowing the range has limited opportunities to detect differential effects.     

Pulsed phase-locked loop technology improvements for greateraccuracy and expanded capabilities

This paper presents the design for a new pulsed phase-locked loop (PPLL) instrument. Earlier phase detection methods are analyzed for potential error sources, and an alternative phase detection method with fewer sources of error is described. This alternative method of phase detection is incorporated into a fully automated PPLL instrument. Data taken with the new system is compared to data taken with an earlier PPLL instrument. This comparison shows that the alternative phase detection does reduce error. The control loop is analyzed for stability and optimization, and a method of automating this optimization is presented. A method of wave-form acquisition using the automated PPLL that permits automatic location of the received echo is also described     

The Ada Environment: A Perspective

Can the Ada environment meet the goals of the DoD high-order language effort? The approach described here promises to be both practical and cost-effective.     

Optical time-domain reflectometry in optical fiber with reflection delay time matched to the period of the optical frequency modulation

A method of optical time-domain reflectrometry in optical fiber is described that uses a single distributed feedback diode laser and a reference reflector. When the period of the frequency modulation of the laser matches the time difference between the reference reflection and the reflection of interest an increase in the noise at the detector occurs. The locations of reflections within the fiber are then mapped to frequencies at which the noise at the detector increases. A sinusoidal frequency modulation is analyzed, and an experiment is described in which the system is used to measure the location and the wavelength of two Bragg gratings located 10 cm apart in an optical fiber. Wavelength measurement is accomplished by temperature tuning the diode laser.