Design of quasi-velocity-matched LiTaO 3 phase modulator

Abstract

ABSTRACT In common electrooptic modulators (EO), the inherent velocity mismatching between the optical wave andmicrowave is the major factor hampering efficient modulation. In this paper, we briefly compare periodically reversedelectrode and domain reversal scheme (two ways of achieving quasi-velocity-matching), then we give the design principleof the EO modulator using domain reversal scheme. At last, we conclude that the bulk LiTaO3 EO modulator can obtainquasi-velocity-matching at special frequency and make the modulation index increase proportionally to the interactionlength.As an experiment, we use a 1 .O6m laser as a light source and a modulating microwave source at 6GHz (16W). Wecan expect that we will get at least 3.0 rads ofmodulation index.keywords quasi-velocity-matching, domain reversal, electrooptic modulation, microstrip resonators I .INTRODI JCTTON To obtain wide optical sideband in photonics device, deep modulation is needed. But in common electroopticmodulators (EO), the inherent velocity mismatching between the optical wave and microwave is the major factorhampering efficient modulation. To solve this problem several methods have been tried by using quasi-velocity-matching.Conventionally, quasi-velocity-matching in traveling wave modulators is realized by periodically reversed electrodesin Z-cut crystals, the electric field changes its phase with respect to the optical wave by x to compensate the accumulatedphase shift due to the velocity mismatch [1]. But there are two deficiencies associated with the phase-reversed electrodeembodiment. First, microwave reflections occurring at the abrupt electrode corner, which may adversely affect the deviceperformance, even though skewing the corners can minimize it [2]. Second, a three-electrode push-pull configuration withelectrode reversals cannot be implemented on X-cut LiTaO3 except the intermittent type (interaction -