Traveling-wave electrooptic modulator

Abstract

An integrated-optics Mach-Zehnder interferometric modulator in LiNbO3 has been designed and fabricated. The electrodes are 3-μm thick asymmetric coplanar striplines formed by ion-beam etching techniques. The push–pull design and the r33 electrooptic coefficient of LiNbO3 are utilized for efficient modulation. Complete modulation is achieved with 6.5 V for the 6-mm long device at 0.83-μm wavelength and with 18 V at 1.3-μm wavelength. The 3-dB bandwidth of the modulator is 3.5 GHz, being limited by the excessive resistive loss of the stripline electrodes. Since this particular modulator retains a dc electrical bias, it performs either as an intensity modulator by applying a π/2 dc phase bias to achieve maximum linearity or as a frequency shifter by changing the dc bias point to π. In addition, we analyzed the principle of operation of the Y junction by observing both the in-phase and the out-of-phase modes of a multimode waveguide modulator.