Broadband and low driving-voltage LiNbO3 optical modulators

Travelling-wave type LiNbO3 (LN) optical modulator structures employing thi cker coplanar waveguide (CPW) electrodes are presented, for achieving a low er driving-voltage and broader bandwidth characteristic with an impedance a nd velocity match condition. To design a high-performance device-structure, a figure of merit p is introduced for travelling-wave type optical modulat ors, which can make an excellent modulator with a smaller value of p. Micro wave characteristics of the modulators with a ridged type LN-substrate are theoretically compared to those of planar-type modulators. As a result, the characteristic-impedance and the product of driving-voltage and interactio n-length of the electrodes in modulators are shown to be almost determined only by the buffer-layer thickness for any modulator-structure under a velo city-matching condition. By utilising a wider gap and accordingly thicker e lectrodes with a ridged LN-substrate, LN modulator structures having a 40 G Hz-band and far less than a 3V driving-voltage have been clarified under a 50 Omega characteristic-impedance system.