Optical intensity modulator using inverted slot line at 60 GHz

The inverted slot line (ISL) structure which has been proposed for millimetre wave LiNbO 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 LiNbO 3 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 μm.