Digital and quasi-linear electrooptic modulators synthesized from directional couplers

By synthesizing from cascaded directional couplers, we propose new designs to achieve digital and quasi-linear electrooptic modulations. For the digital modulator, a nearly perfect on-state or off-state can be obtained in a broad range of modulation voltages. The calculated switching voltage can be as low as the drive voltage of a conventional directional coupler. The quasi-linear modulator is achieved by adding a set of compensating electrodes to a foreshortened directional coupler. Deviation from a linear voltage-intensity relationship of less than 1 percent can be obtained over a 93.5 percent modulation depth. The calculated second harmonic and the third order intermodulation distortions are -18.3 and -32.6 dB, respectively.