Broadband Ti:LiNbO3 Guided-Wave Lumped-Element and Traveling-Wave Interferometric Modulators*

In this paper we report the development and characterization of wideband single-mode Mach-Zehnder interferometric lumped-element and traveling-wave modulators for applications in the 0.85-μm wavelength range. Several papers have been previously published which report the design and performance of Ti-indiffused lumped-element guided-wave electrooptic modulators.1 However, none of these provides sufficient insight for designing a practical modulator for a particular frequency response nor fully evaluates proposed circuit models by investigating a number of modulators with significantly different capacitances, resistances and inductances. Here, these issues are addressed and a simple RLC equivalent circuit is shown to accurately predict measured device performance. A lumped-element modulator with a Vπ = 4 V and a small-signal linear 3-dB bandwidth of 2.75 GHz has been demonstrated. In addition, traveling-wave modulators were fabricated and characterized. A small-signal linear 3-dB bandwidth of 13.2 GHz and a 7.6-μW/MHz figure of merit were measured representing one of the widest bandwidth and most efficient modulators reported. A traveling-wave modulator transmission line analysis predicts a >17-GHz small-signal linear bandwidth for this same device when a different terminating impedance is used.