David H. Smithgall

High-speed noncontact fiber-diameter measurement using forward light scattering

The forward scattering of light by an optical fiber produces an interference fringe pattern, and the fringe period is inversely proportional to the fiber diameter. An electrooptic system has been developed to produce and detect this scattering pattern to provide an instrument which will measure fiber diameter during the drawing operation. The system measures the fiber diameter at a 1-kHz rate with a precision of 0.25 microm and an accuracy of +/-0.25 microm over a range of 50-150-microm diams. The instrument allows the fiber to move laterally in a 1-cm diam window maintaining the above accuracy. The system can be calibrated optically and does not need a standard fiber for this procedure. The instrument has been used for months without the need for recalibration. In addition to the digital diameter output, the system employs a microprocessor to compute mean and standard deviation values for various sample lengths and provides suitable signals for feedback control of fiber diameter.

A Phase-Locked Loop Motor Control System

This paper describes a motor control circuit for a dc motor using phase-locked loop techniques. The purpose of such a control loop is to provide very accurate speed control, repeatability, and synchronization capability.

Graded-index planar dielectric waveguides

Properties of planar dielectric waveguides having a diffusion-induced index of refraction distribution are investigated. It is found that the spatial distribution of modes, group velocity, and mode spectrum of these guides differed qualitatively from the corresponding properties found in a slab waveguide. These results were experimentally verified by measuring the mode spectrum of a dielectric waveguide having an assumed complimentary error-function distribution of refractive index.

An Optical Fiber Diameter Measurement System Using Forward Scattered Light

Forward scattering of light by an optical fiber produces an interference fringe pattern in which the fringe spacing is inversely proportional to the fiber diameter. An electrooptic system has been developed to produce and detect this scattering pattern, thus providing a measure of fiber diameter.

A Microprocessor-Based Statistical Analysis Subsystem

This paper describes a microprocessor-based subsystem which was developed to provide a statistical description of the diameter of an arbitrary length of wire during the drawina or insulation process. The instrument, built around a 4-bit Intel microprocessor, computes the mean and standard deviation of 1000 data samples over a length of wire determined by the setting on a Binary-Coded Decimal (BCD) thumbwheel switch. The sample period may be varied from 2 milliseconds to 10 seconds. The statistical quantities are output on analog channels as well as digital displays. In addition to the statistical computation, the instrument has the option of playing back the data at arbitrary speeds and generatinq histograms of the data samples. The techniques described in this paper can be inexpensively implemented to provide a statistical description of many laboratory or production processes with a minimum of operator intervention.