University of Rochester

American Telephone & Telegraph Co., At&t Bell Laboratories

Janis A Valdmanis

Gerard A Mourou

Steven L Williamson

The longitudinal electro-optic effect is used with an external probe to make voltage measurements on electrical conductors.

Electro-optic measurements of voltage waveforms on electrical conductors

An optical pulse having time-dependent spectral variation is modulated by a time-dependent signal so that, upon determination of the spectral content of the modulated pulse, a representation of the signal can be obtained. Frequency in the optical pulse preferably varies essentially unidirectionally, i.e., aside from noise, each frequency is encountered just once as, e.g., in a linear relationship. Such an optical pulse can be produced by passing a short laser pulse through a dispersive medium such as, e.g., an optical fiber whose zero-dispersion wavelength is away from wavelengths to be dispersed. Modulation of the optical pulse may be by electrooptic interaction. The technique can be used for the characterization of device and material responses; envisaged also are communications applications.

Device and method for signal transmission and optical communications

Electrical signals are measured (analyzed and displayed) with subpicosecond resolution by electro-optic sampling of the signal in an electro-optic crystal, the index of which changes in response to the electric field produced by the signal, in accordance with the Pockels effect. The crystal is disposed adjacent to and in the fringe field of a line on a substrate, which may be part of an integrated circuit, for measuring signals propagating along the line during the operation of the circuit. A beam of short optical (laser) sampling pulses in the picosecond range is focused preferably close to the surface of the crystal and perpendicular to the optical axis of the crystal. The optical pulses transmitted through the crystal are processed to provide a display affording a measurement of the electrical signal.

Measurement of electrical signals with subpicosecond resolution

Electrical signals are measured (analyzed and displayed) with picosecond resolution by the electrooptic sampling of the signal being analyzed in a traveling wave Pockels cell. Sampling pulses, from an optical pulse generator such as a colliding pulse mode-locked laser, of subpicosecond duration are transmitted through the cell as polarized light and translated into a difference output corresponding to the difference in amplitude between the transmitted and rejected components of the polarized light. The signals, synchronous with the optical sampling pulses, are generated to propagate along the cell in a direction transverse to the transmission of the optical sampling pulses and in variably delayed relationship therewith. A separate beam of the optical pulses is desirably chopped and used to activate a photoconductive device which produces the signals. The difference output is processed, preferably by a lock-in amplifier and signal averager; the lock-in amplifier being synchronized with the chopping of the launched pulses, and displayed on a time base synchronous with the variable delay of the pulses. Accordingly, the signal is displayed on an expanded time scale for measurement and other analysis. The response of photodetectors, photoconductive switches and other ultrafast light activated devices can be determined, when these devices are used as the source of the signals being analyzed and displayed.

Measurement of electrical signals with picosecond resolution

Electrical signals are measured (analyzed and displayed) with picosecond resolution and sensitivity in the microvolt (less than 100 microvolts) range by electron-optically sampling the signal. Sampling electron bursts are produced in response to a train of subpicosecond optical pulses. A beam of these electron bursts samples successive portions of the signal as it is transmitted as a travelling wave along deflection plates which act as a transmission line. The bursts are deflected in accordance with the amplitude of the successive portions of the signal and translated into spots of light, as on a phosphor screen. The deflection is significantly less than the diameter of the spot. The deviation of the spot with respect to the position thereof in the absence of the signal on the deflection plates is translated into a difference output. The signal to be analyzed is generated, synchronously with the optical pulses, to propagate along the deflection plates in variably delayed relationship therewith. The signal is optically-induced using a separate beam of the optical pulses which is desirably chopped into optical pulses. The difference output is processed, preferably by a lock-in amplifier and signal averager; the lock-in amplifier being synchronized with the chopping of the beam into the optical pulses, and displayed on a time base synchronous with the variable delay of the optical pulses. Accordingly, the signal is displayed on an expanded time scale for measurement and other analysis.

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Westfield, NJ, United States of America

Janis A Valdmanis