Phase Velocity Estimation of a Microstrip Line in a Stoichiometric Periodically Domain-Inverted Modulator Using Electro-Optic Sampling Technique

We estimate the phase velocity of a modulation microwave in a quasi-velocity-matched (QVM) electro-optic (EO) phase modulator (QVM-EOM) using EO sampling which is accurate and the most reliable technique for measuring voltage waveforms at an electrode. The substrate of the measured QVM-EOM is a stoichiometric periodically domain-inverted LiTaO3 crystal. The electric field of a standing wave in a resonant microstrip line (width: 0.5 mm, height: 0.5 mm) is measured by employing a CdTe crystal as an EO sensor. The wavelength of the traveling microwave at 16.0801 GHz is determined as 3.33 mm by fitting the theoretical curve to the measured electric field distribution. The phase velocity is estimated as =5.35×107 m/s, though there exists about 5% systematic error due to the perturbation by the EO sensor. Relative dielectric constant of =41.5 is led as the maximum likelihood value that derives the estimated phase velocity.