James R. Andrews

Inexpensive laser diode pulse generator for optical waveguide studies

An inexpensive GaAs laser diode pulse generator is presented. This generator has found application in the evaluation of optical pulse dispersion in glass fiber optical waveguide studies. It is capable of producing optical impulses as narrow as 110 psec at a wavelength of 0.9 μ and a pulse repetition rate of 50 kHz. With a slight modification, it may be used to produce optical pulses of considerably longer duration at reduced repetition rates.

Optically strobed sampling oscilloscope

Describes an optically strobed sampling oscilloscope which uses optical pulses from a GaAs laser diode to strobe a Cr-doped GaAs photoconductor which serves as a sampling gate. This sampling gate has been used with a commercial sampling oscilloscope to provide a sampling measurement capability that can measure higher voltages than conventional samplers and does not exhibit strobe pulse kickout. Preliminary tests indicate a time resolution, limited by the width of the optical pulse used, for about 100 ps.

Reference Waveform Flat Pulse Generator

The NBS Reference Flat Pulse Generator (RFPG) is used to transfer dc voltage and resistance standards to the nanosecond domain. It provides a step amplitude of 1.000 V (open circuit) from a source impedance of 50.0¿. The transition duration is 600 ps, and all perturbations are damped out to less than ±10 mV within 5 ns. It can also be used as a time interval transfer standard.

Random Sampling Oscilloscope for the Observation of Mercury Switch Closure Transition Times

With the advent of new miniaturized mercury (Hg) switches with reputed transition times of the order of 10 ps, interest has been rekindled in their use in high-peed pulse measurements. Since there is no pretrigger signal available from a Hg switch, normal sequential sampling techniques are not useable to measure the fast Hg switch transition time. For this reason, a new random sampling time base unit was designed to perform these measurements at the low repetition rate of Hg switches. The time base may be used with commercial sampling oscilloscope systems through suitable interconnection terminals or possible interface equipment. It features three selectable time windows of 1 jus, 100 ns, and 10 ns. Using its time magnifier, the fastest sweep rate is 10 ps/cm. A variable trigger lead time control is provided. The trigger sensitivity is 5 mV.

Precision Picosecond-Pulse Measurements Using a High-Quality Superconducting Delay Line

A high-quality superconducting delay line now makes it possible to perform direct oscillographic measurements of the picosecond transition times of very fast electrical signals that do not furnish pretriggers. A 15-m superconducting delay line package has been assembled. The package consists of connectors, connector adapters, normally conducting input/output air lines, and a 15 m length of a miniature 1.6-mm superconducting coaxial transmission line. The package exhibits an attenuation of 0.8 dB at 10 GHz and a system 10-90 percent transition time of 18 ps. Some applications of this delay line are shown. They include the measurement of the pulse output from a mercury switch and the transient response of a traveling-wave oscilloscope.

Improved Bias Supply for Tunnel-Diode Picosecond Pulse Generators

An improved bias supply for tunnel-diode (TD) picosecond-pulse generators is described. The supply is stable with temperature and, in a commercial 35-ps (nominal) risetime tunneldiode pulse generator/sampling oscilloscope system, has produced a 4:1 reduction in time-base jitter and 2:1 reduction in time-base drift. Also described is a tunnel-diode pulse generator, which, when used with the bias supply, produces a stable pulse having a flat-top sag of no more than 2 percent in 1 ?s.

Pulsed Wavemeter Timing Reference for Sampling Oscilloscope Calibration

A pulsed wavemeter technique is described that is useful as a source of microwave frequency sine waves for the time base calibration of sampling oscilloscopes.

Electrically strobed optical waveform sampling oscilloscope

A new instrument for measuring optical waveforms is described. It is an optical sampling oscilloscope employing a GaAs photoconductive sampling gate and an electrical sampling strobe. The basic theory of operation is derived. A 100‐psec rise‐time rudimentary prototype has been built and results of measurements of a GaAs laser diode pulse are presented.

Construction of a Broadband Universal Sampling Head

A broadband, feed-through, sampling head with a transition duration of 26 ps has been built using a wide-band, thin-film mixer from an Hewlett-Packard (H-P) frequency counter. This head can be used with both Hewlett-Packard (H-P) and Tektronix sampling oscilloscopes. Responses of this head, and other sampling heads, to a standard input step waveform are shown.

Directional-Coupler Technique for Triggering a Tunnel Diode

Present tunnel diode (TD) pulse generators have distortions in the pulse baseline and topline due to feedthrough of the triggering signal. This paper presents a new technique for reducing the trigger-induced distortions. A directional coupler is used to couple the trigger signal to the TD.