Electrical and Optical Characteristics of 20 GHz Ti:LiNbO3 Traveling Wave Intensity Modulator,
Abstract
The bandwidth of Ti:LiNbO3 traveling wave (TW) optical modulators may be enhanced by improving the phase match between the microwave and optical signals. This has been accomplished in the coplanar waveguide (CPW) configuration by use of a shielding plane and in the coplanar strips (CPS) configuration by use of thick electrodes. In the phase matched condition, the device bandwidth would be limited by only the resistive electrode loss, provided that there is no power leakage from the fundamental coplanar mode to the dielectric substrate modes of LiNbO3. We have observed and modeled this leakage that occurs in LiNbO3 traveling wave modulators. Below we describe our model and demonstrate a 20 GHz bandwidth optical modulator in the CPW configuration with thick electrodes without any power leakage over a 40 GHz span. The V sub pi, for this device was 5 V at an operating wavelength of 1.3 micrometer. The fundamental mode of a coplanar waveguide can become leaky by coupling to substrate modes (surface waves) when the effective index of the substrate mode is larger than that of the coplanar mode. Phase match is achieved in the process by a tilt of the substrate mode wavevector relative to the axial direction of the coplanar mode and leakage occurs to both sides of the coplanar guide. To model this leakage, we consider c-cut slabs of LiNbO3 which May Or may not have a conductive layer (electrode) on top. The slab has a thickness h and is considered to be semi-finite in width. The dispersion curves for the substrate modes are shown.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1992
- Accession Number
- ADP008154
Entities
People
- A. S. Greenblatt
- C. H. Bulmer
- G. K. Gopalakrishnan
- R. W. Mcelhanon
- W. K. Burns
Organizations
- United States Naval Research Laboratory