The inverted slot line (ISL) structure which has been proposed for millimetre wave LjNbO(3) optical modulator is found to be very simple in structure, and is also capable of easily achieving a perfect velocity matching between carrier and modulating waves. This paper describes the analysis of the ISL based on the spectral domain approach and the practical development of a Mach-Zehnder Ti-diffused LiNbO3 optical intensity modulator using the ISL at 60 GHz. To launch millimetre waves into the ISL structure two types of transitions have been developed successfully. In one type, a balun which is made from a semi-rigid coaxial cable is used to feed millimetre waves into the ISL. In another type, a non-radiative dielectric (NRD) waveguide which can provide the total integration of the modulator with millimetre wave integrated circuits is used to excite the ISL structure ensuring minimum transition losses. A modulator response of 0.17 W-1 could be obtained at 60 GHz using a Mach-Zehnder interferometer with a rather poor extinction ratio at an optical wavelength of 0.633 mu m. References: 8
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