Abstract

We describe a new broadband microwave spectroscopy technique based on the transient radiation from optoelectronically pulsed integrated antennas. We use exponentially tapered coplanar stripline antennas fabricated on silicon-on sapphire substrates [1]. The coherent microwave transient spectroscopy (COMITS) experiment consists of a transmitter and a receiver with the sample to be characterized located between them. Optical pulses of 2.5 ps duration at 532 nm wavelength are used to excite the transmitter and to photoconductively sample the received voltage signal. With no sample between the two antennas, a typical waveform consists of a 7 ps wide central peak with two negative peaks separated by 17 ps. The amplitude spectrum of the received signal, obtained by Fourier transforming the temporal data, has components extending up to 150 GHz and tends to zero at low frequencies. For a standard COMITS measurement two recordings are taken with and without the sample. The amplitude and phase of the transmission function of the sample are derived by comparing the Fourier transforms of the two sets of temporal data. We use samples of well known and predictable behaviour to characterize the experimental set-up. For instance, the measured amplitude and phase for Fabry-Perot interferometers display the expected spectral dependence determined by the plate separation. Measurements of the loss and dispersion properties of materials were also performed with the spectroscopy apparatus, and results obtained for fused silica over the 10-125 GHz band will be presented.

© 1988 Optical Society of America