Abstract

Recently, traveling wave (TW) LiNbO₃ optical modulators with performance extending well into the millimeter-wave frequency spectrum have been fabricated by engineering a near velocity match between microwave and optical signals [1,2]. In these devices, the dimensions of the coplanar waveguide (CPW) electrode in the active section are typically very narrow; for the device reported in ref. 1, the center strip width (w) = 8 μm and gap width (g) = 15 μm. To facilitate external microwave and optical access to the modulator, CPW tapers and bends are designed in conjunction with the active section of the device. Previously, high frequency operation of these devices, in the velocity matched condition, has been believed to be limited by only the conductor loss ($\sqrt{f}$ loss) of the electrode. However, other losses such as dielectric loss (proportional to f) that stems from the loss tangent of the material and radiative loss that stems from radiation from discontinuities such as tapers and bends may also become significant at high-frequencies. Since tapers and bends are integral components of the device, losses that occur in these sections affect the overall device response. We investigate such losses in a TW modulator [1] and assign independent loss coefficients to different sections of the device.

© 1993 Optical Society of America