Abstract
Electro-optic (E-O) sampling is a useful technique to study the electric-field distribution in a GaAs microstrip circuit.1 Such sampling has an extremely wide bandwidth capability and can perform the measurement without physically or electrically contacting the device. We present here the interference effect associated with E-O sampling in GaAs microstrips.2 The refraction index of GaAs is rather high (>3.5); thus, a substantial amount of light (30% energy for normal incident) is reflected from the top surface of GaAs, which will interfere with light reflected from the ground plane. The interference effect is significant if the laser-pulse duration used for E-O sampling is longer than or comparable to the round-trip transit time of the light wave in the GaAs substrate. Thus, the magnitude of the sampled signal strongly depends on the local substrate thickness, which can cause a problem in calibrating the amplitude of the microwave signal to be sampled. For a conventional E-O sampling detection scheme using an analyzer, the modulation of light intensity applied to the photodetector can be expressed by:
© 1991 Optical Society of America
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