Abstract
Domain inversion is used in a simple fashion to improve significantly the performance of a waveguide electro-optic modulator in z-cut LiNbO(3). The waveguide arms of the Mach-Zehnder interferometer are placed in opposite domain-oriented regions under the same, narrower and more efficient electrode, so that opposite phase shifts (push-pull effect) can still be achieved despite the arms being subjected to the same electric field. Switching voltages close to 2 V are obtained, which allow 10Gb/s modulation with inexpensive drivers, such as those used for electro-absorption modulators, which deliver driving voltages well below 3V.
Highlights
Over the last year the demand of integrated electro-optic LiNbO 3 modulators has been steadily increasing
Domain inversion is used in a simple fashion to improve significantly the performance of a waveguide electro-optic modulator in z-cut LiNbO3
The waveguide arms of the Mach-Zehnder interferometer are placed in opposite domain-oriented regions under the same, narrower and more efficient electrode, so that opposite phase shifts can still be achieved despite the arms being subjected to the same electric field
Summary
Over the last year the demand of integrated electro-optic LiNbO 3 modulators has been steadily increasing. Domain engineering of z-cut LiNbO 3 structures has been proposed to produce large bandwidth and very low voltage modulators where the pushpull effect in the Mach-Zehnder interferometric structure has been obtained by placing the waveguides in opposite-sign electro-optic coefficient regions (i.e. opposite-oriented domains) and under the same electric field [9]. The optical fields in the two waveguides experience an opposite phase shift despite being subjected to the same electric field [9], the hot travelling wave electrode can either be of Mach-Zehnder type (i.e. it follows the shape of the optical layout) [10] or a single straight electrode as in this work This is in contrast with previous high frequency modulating structures in single domain crystals where the two waveguides are placed under two different electrodes having different (usually opposite sign) voltages [1]. With respect to previous modulating structures in single domain crystal, the proposed DI symmetric scheme allows to achieve at the same time maximum-efficiency, chirp-free and single-drive operation all at once
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