Characterization Of Frequency Dispersion In Ti-Indiffused Lithium Niobate Optical Devices

Characterization of frequency dispersion in Ti-indiffused lithium niobate optical devicesJ. L. Nightingale, R. A. Becker, P. C. Willis and J. S. Vrhel Crystal Technology Inc., 1040 E. Meadow Circle, Palo Alto, CA, USA 94303ABSTRACTThe frequency dispersion of integrated optic interferometers fabricated on different lithium niobate cuts is characterized. Only the configuration that uses the r33 electrooptic coefficient is well behaved.1. INTRODUCTIONRecently there have been several reports1 * 2^ of Ti-indiffused LiNbO3 waveguide devices proposed and demonstrated on crystal orientations which utilize other than the r33 electrooptic coefficient. These reports include devices which propagate light in the z-direction for higher power handling capabilities 2 and for polarization modulation.3 In this paper we characterize the frequency dispersion displayed by the various combinations of electrooptic coefficients and substrate orientations. It is found that only the r33 electrooptic coefficient results in a well behaved, broadband frequency response.2. EXPERIMENTAL TECHNIQUE AND RESULTSIn this work we fabricated integrated optic Mach-Zehnder interferometers on the following LiNb03 substrate orientations: X-cut, Y-propagating; X-cut, Z-propagating; and Z-cut, X- propagating. The waveguides were formed using the standard Ti-indiffusion technique. Fabrication parameters chosen yielded single-mode optical waveguides at 0.83 |nm. The devices used center-tapped, 12-mm-long push-pull electrodes.4 The center electrode in this configuration was 35 |am wide and the two adjacent ground electrodes were each 50 ^im wide. The Cr/Au metallization thickness was 1 pm. The waveguides were centered in the electrode gap which was 6.0 ± 0.7 |im wide. The electrode capacitances at 1 MHz ranged from 9.5 pF to 15.5 pF depending on the substrate orientation and electrode gap. Figure 1 illustrates the center-tapped Mach-Zehnder geometry and defines the coordinate system used throughout the paper.